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llvm-project/llvm/test/Transforms/InstCombine/mem-gep-zidx.ll

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[InstCombine] Remove unnecessary variable indexing into single-element arrays This change addresses a deficiency pointed out in PR22629. To copy from the bug report: [from the bug report] Consider this code: int f(int x) { int a[] = {12}; return a[x]; } GCC knows to optimize this to movl $12, %eax ret The code generated by recent Clang at -O3 is: movslq %edi, %rax movl .L_ZZ1fiE1a(,%rax,4), %eax retq .L_ZZ1fiE1a: .long 12 # 0xc [end from the bug report] This definitely seems worth fixing. I've also seen this kind of code before (as the base case of generic vector wrapper templates with one element). The general idea is to look at the GEP feeding a load or a store, which has some variable as its first non-zero index, and determine if that index must be zero (or else an out-of-bounds access would occur). We can do this for allocas and globals with constant initializers where we know the maximum size of the underlying object. When we find such a GEP, we create a new one for the memory access with that first variable index replaced with a constant zero. Even if we can't eliminate the memory access (and sometimes we can't), it is still useful because it removes unnecessary indexing calculations. llvm-svn: 229959
2015-02-20 11:05:53 +08:00
; RUN: opt -S -instcombine < %s | FileCheck %s
target datalayout = "E-m:e-i64:64-n32:64"
target triple = "powerpc64-unknown-linux-gnu"
@f.a = private unnamed_addr constant [1 x i32] [i32 12], align 4
@f.b = private unnamed_addr constant [1 x i32] [i32 55], align 4
Fix a typo in rL265762 I accidentally replaced `mayBeOverridden` with `!isInterposable`. Remove the negation and add a test case that would've caught this. Many thanks to Håkan Hjort for spotting this! llvm-svn: 266551
2016-04-17 12:30:43 +08:00
@f.c = linkonce unnamed_addr alias [1 x i32], [1 x i32]* @f.b
[InstCombine] Remove unnecessary variable indexing into single-element arrays This change addresses a deficiency pointed out in PR22629. To copy from the bug report: [from the bug report] Consider this code: int f(int x) { int a[] = {12}; return a[x]; } GCC knows to optimize this to movl $12, %eax ret The code generated by recent Clang at -O3 is: movslq %edi, %rax movl .L_ZZ1fiE1a(,%rax,4), %eax retq .L_ZZ1fiE1a: .long 12 # 0xc [end from the bug report] This definitely seems worth fixing. I've also seen this kind of code before (as the base case of generic vector wrapper templates with one element). The general idea is to look at the GEP feeding a load or a store, which has some variable as its first non-zero index, and determine if that index must be zero (or else an out-of-bounds access would occur). We can do this for allocas and globals with constant initializers where we know the maximum size of the underlying object. When we find such a GEP, we create a new one for the memory access with that first variable index replaced with a constant zero. Even if we can't eliminate the memory access (and sometimes we can't), it is still useful because it removes unnecessary indexing calculations. llvm-svn: 229959
2015-02-20 11:05:53 +08:00
define signext i32 @test1(i32 signext %x) #0 {
entry:
%idxprom = sext i32 %x to i64
[opaque pointer type] Add textual IR support for explicit type parameter to getelementptr instruction One of several parallel first steps to remove the target type of pointers, replacing them with a single opaque pointer type. This adds an explicit type parameter to the gep instruction so that when the first parameter becomes an opaque pointer type, the type to gep through is still available to the instructions. * This doesn't modify gep operators, only instructions (operators will be handled separately) * Textual IR changes only. Bitcode (including upgrade) and changing the in-memory representation will be in separate changes. * geps of vectors are transformed as: getelementptr <4 x float*> %x, ... ->getelementptr float, <4 x float*> %x, ... Then, once the opaque pointer type is introduced, this will ultimately look like: getelementptr float, <4 x ptr> %x with the unambiguous interpretation that it is a vector of pointers to float. * address spaces remain on the pointer, not the type: getelementptr float addrspace(1)* %x ->getelementptr float, float addrspace(1)* %x Then, eventually: getelementptr float, ptr addrspace(1) %x Importantly, the massive amount of test case churn has been automated by same crappy python code. I had to manually update a few test cases that wouldn't fit the script's model (r228970,r229196,r229197,r229198). The python script just massages stdin and writes the result to stdout, I then wrapped that in a shell script to handle replacing files, then using the usual find+xargs to migrate all the files. update.py: import fileinput import sys import re ibrep = re.compile(r"(^.*?[^%\w]getelementptr inbounds )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))") normrep = re.compile( r"(^.*?[^%\w]getelementptr )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))") def conv(match, line): if not match: return line line = match.groups()[0] if len(match.groups()[5]) == 0: line += match.groups()[2] line += match.groups()[3] line += ", " line += match.groups()[1] line += "\n" return line for line in sys.stdin: if line.find("getelementptr ") == line.find("getelementptr inbounds"): if line.find("getelementptr inbounds") != line.find("getelementptr inbounds ("): line = conv(re.match(ibrep, line), line) elif line.find("getelementptr ") != line.find("getelementptr ("): line = conv(re.match(normrep, line), line) sys.stdout.write(line) apply.sh: for name in "$@" do python3 `dirname "$0"`/update.py < "$name" > "$name.tmp" && mv "$name.tmp" "$name" rm -f "$name.tmp" done The actual commands: From llvm/src: find test/ -name *.ll | xargs ./apply.sh From llvm/src/tools/clang: find test/ -name *.mm -o -name *.m -o -name *.cpp -o -name *.c | xargs -I '{}' ../../apply.sh "{}" From llvm/src/tools/polly: find test/ -name *.ll | xargs ./apply.sh After that, check-all (with llvm, clang, clang-tools-extra, lld, compiler-rt, and polly all checked out). The extra 'rm' in the apply.sh script is due to a few files in clang's test suite using interesting unicode stuff that my python script was throwing exceptions on. None of those files needed to be migrated, so it seemed sufficient to ignore those cases. Reviewers: rafael, dexonsmith, grosser Differential Revision: http://reviews.llvm.org/D7636 llvm-svn: 230786
2015-02-28 03:29:02 +08:00
%arrayidx = getelementptr inbounds [1 x i32], [1 x i32]* @f.a, i64 0, i64 %idxprom
[opaque pointer type] Add textual IR support for explicit type parameter to load instruction Essentially the same as the GEP change in r230786. A similar migration script can be used to update test cases, though a few more test case improvements/changes were required this time around: (r229269-r229278) import fileinput import sys import re pat = re.compile(r"((?:=|:|^)\s*load (?:atomic )?(?:volatile )?(.*?))(| addrspace\(\d+\) *)\*($| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$)") for line in sys.stdin: sys.stdout.write(re.sub(pat, r"\1, \2\3*\4", line)) Reviewers: rafael, dexonsmith, grosser Differential Revision: http://reviews.llvm.org/D7649 llvm-svn: 230794
2015-02-28 05:17:42 +08:00
%0 = load i32, i32* %arrayidx, align 4
[InstCombine] Remove unnecessary variable indexing into single-element arrays This change addresses a deficiency pointed out in PR22629. To copy from the bug report: [from the bug report] Consider this code: int f(int x) { int a[] = {12}; return a[x]; } GCC knows to optimize this to movl $12, %eax ret The code generated by recent Clang at -O3 is: movslq %edi, %rax movl .L_ZZ1fiE1a(,%rax,4), %eax retq .L_ZZ1fiE1a: .long 12 # 0xc [end from the bug report] This definitely seems worth fixing. I've also seen this kind of code before (as the base case of generic vector wrapper templates with one element). The general idea is to look at the GEP feeding a load or a store, which has some variable as its first non-zero index, and determine if that index must be zero (or else an out-of-bounds access would occur). We can do this for allocas and globals with constant initializers where we know the maximum size of the underlying object. When we find such a GEP, we create a new one for the memory access with that first variable index replaced with a constant zero. Even if we can't eliminate the memory access (and sometimes we can't), it is still useful because it removes unnecessary indexing calculations. llvm-svn: 229959
2015-02-20 11:05:53 +08:00
ret i32 %0
; CHECK-LABEL: @test1
; CHECK: ret i32 12
}
declare void @foo(i64* %p)
define void @test2(i32 signext %x, i64 %v) #0 {
entry:
%p = alloca i64
%idxprom = sext i32 %x to i64
[opaque pointer type] Add textual IR support for explicit type parameter to getelementptr instruction One of several parallel first steps to remove the target type of pointers, replacing them with a single opaque pointer type. This adds an explicit type parameter to the gep instruction so that when the first parameter becomes an opaque pointer type, the type to gep through is still available to the instructions. * This doesn't modify gep operators, only instructions (operators will be handled separately) * Textual IR changes only. Bitcode (including upgrade) and changing the in-memory representation will be in separate changes. * geps of vectors are transformed as: getelementptr <4 x float*> %x, ... ->getelementptr float, <4 x float*> %x, ... Then, once the opaque pointer type is introduced, this will ultimately look like: getelementptr float, <4 x ptr> %x with the unambiguous interpretation that it is a vector of pointers to float. * address spaces remain on the pointer, not the type: getelementptr float addrspace(1)* %x ->getelementptr float, float addrspace(1)* %x Then, eventually: getelementptr float, ptr addrspace(1) %x Importantly, the massive amount of test case churn has been automated by same crappy python code. I had to manually update a few test cases that wouldn't fit the script's model (r228970,r229196,r229197,r229198). The python script just massages stdin and writes the result to stdout, I then wrapped that in a shell script to handle replacing files, then using the usual find+xargs to migrate all the files. update.py: import fileinput import sys import re ibrep = re.compile(r"(^.*?[^%\w]getelementptr inbounds )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))") normrep = re.compile( r"(^.*?[^%\w]getelementptr )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))") def conv(match, line): if not match: return line line = match.groups()[0] if len(match.groups()[5]) == 0: line += match.groups()[2] line += match.groups()[3] line += ", " line += match.groups()[1] line += "\n" return line for line in sys.stdin: if line.find("getelementptr ") == line.find("getelementptr inbounds"): if line.find("getelementptr inbounds") != line.find("getelementptr inbounds ("): line = conv(re.match(ibrep, line), line) elif line.find("getelementptr ") != line.find("getelementptr ("): line = conv(re.match(normrep, line), line) sys.stdout.write(line) apply.sh: for name in "$@" do python3 `dirname "$0"`/update.py < "$name" > "$name.tmp" && mv "$name.tmp" "$name" rm -f "$name.tmp" done The actual commands: From llvm/src: find test/ -name *.ll | xargs ./apply.sh From llvm/src/tools/clang: find test/ -name *.mm -o -name *.m -o -name *.cpp -o -name *.c | xargs -I '{}' ../../apply.sh "{}" From llvm/src/tools/polly: find test/ -name *.ll | xargs ./apply.sh After that, check-all (with llvm, clang, clang-tools-extra, lld, compiler-rt, and polly all checked out). The extra 'rm' in the apply.sh script is due to a few files in clang's test suite using interesting unicode stuff that my python script was throwing exceptions on. None of those files needed to be migrated, so it seemed sufficient to ignore those cases. Reviewers: rafael, dexonsmith, grosser Differential Revision: http://reviews.llvm.org/D7636 llvm-svn: 230786
2015-02-28 03:29:02 +08:00
%arrayidx = getelementptr inbounds i64, i64* %p, i64 %idxprom
[InstCombine] Remove unnecessary variable indexing into single-element arrays This change addresses a deficiency pointed out in PR22629. To copy from the bug report: [from the bug report] Consider this code: int f(int x) { int a[] = {12}; return a[x]; } GCC knows to optimize this to movl $12, %eax ret The code generated by recent Clang at -O3 is: movslq %edi, %rax movl .L_ZZ1fiE1a(,%rax,4), %eax retq .L_ZZ1fiE1a: .long 12 # 0xc [end from the bug report] This definitely seems worth fixing. I've also seen this kind of code before (as the base case of generic vector wrapper templates with one element). The general idea is to look at the GEP feeding a load or a store, which has some variable as its first non-zero index, and determine if that index must be zero (or else an out-of-bounds access would occur). We can do this for allocas and globals with constant initializers where we know the maximum size of the underlying object. When we find such a GEP, we create a new one for the memory access with that first variable index replaced with a constant zero. Even if we can't eliminate the memory access (and sometimes we can't), it is still useful because it removes unnecessary indexing calculations. llvm-svn: 229959
2015-02-20 11:05:53 +08:00
store i64 %v, i64* %arrayidx
call void @foo(i64* %p)
ret void
; CHECK-LABEL: @test2
; CHECK: %p = alloca i64
; CHECK: store i64 %v, i64* %p
; CHECK: ret void
}
define signext i32 @test3(i32 signext %x, i1 %y) #0 {
entry:
%idxprom = sext i32 %x to i64
%p = select i1 %y, [1 x i32]* @f.a, [1 x i32]* @f.b
[opaque pointer type] Add textual IR support for explicit type parameter to getelementptr instruction One of several parallel first steps to remove the target type of pointers, replacing them with a single opaque pointer type. This adds an explicit type parameter to the gep instruction so that when the first parameter becomes an opaque pointer type, the type to gep through is still available to the instructions. * This doesn't modify gep operators, only instructions (operators will be handled separately) * Textual IR changes only. Bitcode (including upgrade) and changing the in-memory representation will be in separate changes. * geps of vectors are transformed as: getelementptr <4 x float*> %x, ... ->getelementptr float, <4 x float*> %x, ... Then, once the opaque pointer type is introduced, this will ultimately look like: getelementptr float, <4 x ptr> %x with the unambiguous interpretation that it is a vector of pointers to float. * address spaces remain on the pointer, not the type: getelementptr float addrspace(1)* %x ->getelementptr float, float addrspace(1)* %x Then, eventually: getelementptr float, ptr addrspace(1) %x Importantly, the massive amount of test case churn has been automated by same crappy python code. I had to manually update a few test cases that wouldn't fit the script's model (r228970,r229196,r229197,r229198). The python script just massages stdin and writes the result to stdout, I then wrapped that in a shell script to handle replacing files, then using the usual find+xargs to migrate all the files. update.py: import fileinput import sys import re ibrep = re.compile(r"(^.*?[^%\w]getelementptr inbounds )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))") normrep = re.compile( r"(^.*?[^%\w]getelementptr )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))") def conv(match, line): if not match: return line line = match.groups()[0] if len(match.groups()[5]) == 0: line += match.groups()[2] line += match.groups()[3] line += ", " line += match.groups()[1] line += "\n" return line for line in sys.stdin: if line.find("getelementptr ") == line.find("getelementptr inbounds"): if line.find("getelementptr inbounds") != line.find("getelementptr inbounds ("): line = conv(re.match(ibrep, line), line) elif line.find("getelementptr ") != line.find("getelementptr ("): line = conv(re.match(normrep, line), line) sys.stdout.write(line) apply.sh: for name in "$@" do python3 `dirname "$0"`/update.py < "$name" > "$name.tmp" && mv "$name.tmp" "$name" rm -f "$name.tmp" done The actual commands: From llvm/src: find test/ -name *.ll | xargs ./apply.sh From llvm/src/tools/clang: find test/ -name *.mm -o -name *.m -o -name *.cpp -o -name *.c | xargs -I '{}' ../../apply.sh "{}" From llvm/src/tools/polly: find test/ -name *.ll | xargs ./apply.sh After that, check-all (with llvm, clang, clang-tools-extra, lld, compiler-rt, and polly all checked out). The extra 'rm' in the apply.sh script is due to a few files in clang's test suite using interesting unicode stuff that my python script was throwing exceptions on. None of those files needed to be migrated, so it seemed sufficient to ignore those cases. Reviewers: rafael, dexonsmith, grosser Differential Revision: http://reviews.llvm.org/D7636 llvm-svn: 230786
2015-02-28 03:29:02 +08:00
%arrayidx = getelementptr inbounds [1 x i32], [1 x i32]* %p, i64 0, i64 %idxprom
[opaque pointer type] Add textual IR support for explicit type parameter to load instruction Essentially the same as the GEP change in r230786. A similar migration script can be used to update test cases, though a few more test case improvements/changes were required this time around: (r229269-r229278) import fileinput import sys import re pat = re.compile(r"((?:=|:|^)\s*load (?:atomic )?(?:volatile )?(.*?))(| addrspace\(\d+\) *)\*($| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$)") for line in sys.stdin: sys.stdout.write(re.sub(pat, r"\1, \2\3*\4", line)) Reviewers: rafael, dexonsmith, grosser Differential Revision: http://reviews.llvm.org/D7649 llvm-svn: 230794
2015-02-28 05:17:42 +08:00
%0 = load i32, i32* %arrayidx, align 4
[InstCombine] Remove unnecessary variable indexing into single-element arrays This change addresses a deficiency pointed out in PR22629. To copy from the bug report: [from the bug report] Consider this code: int f(int x) { int a[] = {12}; return a[x]; } GCC knows to optimize this to movl $12, %eax ret The code generated by recent Clang at -O3 is: movslq %edi, %rax movl .L_ZZ1fiE1a(,%rax,4), %eax retq .L_ZZ1fiE1a: .long 12 # 0xc [end from the bug report] This definitely seems worth fixing. I've also seen this kind of code before (as the base case of generic vector wrapper templates with one element). The general idea is to look at the GEP feeding a load or a store, which has some variable as its first non-zero index, and determine if that index must be zero (or else an out-of-bounds access would occur). We can do this for allocas and globals with constant initializers where we know the maximum size of the underlying object. When we find such a GEP, we create a new one for the memory access with that first variable index replaced with a constant zero. Even if we can't eliminate the memory access (and sometimes we can't), it is still useful because it removes unnecessary indexing calculations. llvm-svn: 229959
2015-02-20 11:05:53 +08:00
ret i32 %0
; CHECK-LABEL: @test3
[opaque pointer type] Add textual IR support for explicit type parameter to getelementptr instruction One of several parallel first steps to remove the target type of pointers, replacing them with a single opaque pointer type. This adds an explicit type parameter to the gep instruction so that when the first parameter becomes an opaque pointer type, the type to gep through is still available to the instructions. * This doesn't modify gep operators, only instructions (operators will be handled separately) * Textual IR changes only. Bitcode (including upgrade) and changing the in-memory representation will be in separate changes. * geps of vectors are transformed as: getelementptr <4 x float*> %x, ... ->getelementptr float, <4 x float*> %x, ... Then, once the opaque pointer type is introduced, this will ultimately look like: getelementptr float, <4 x ptr> %x with the unambiguous interpretation that it is a vector of pointers to float. * address spaces remain on the pointer, not the type: getelementptr float addrspace(1)* %x ->getelementptr float, float addrspace(1)* %x Then, eventually: getelementptr float, ptr addrspace(1) %x Importantly, the massive amount of test case churn has been automated by same crappy python code. I had to manually update a few test cases that wouldn't fit the script's model (r228970,r229196,r229197,r229198). The python script just massages stdin and writes the result to stdout, I then wrapped that in a shell script to handle replacing files, then using the usual find+xargs to migrate all the files. update.py: import fileinput import sys import re ibrep = re.compile(r"(^.*?[^%\w]getelementptr inbounds )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))") normrep = re.compile( r"(^.*?[^%\w]getelementptr )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))") def conv(match, line): if not match: return line line = match.groups()[0] if len(match.groups()[5]) == 0: line += match.groups()[2] line += match.groups()[3] line += ", " line += match.groups()[1] line += "\n" return line for line in sys.stdin: if line.find("getelementptr ") == line.find("getelementptr inbounds"): if line.find("getelementptr inbounds") != line.find("getelementptr inbounds ("): line = conv(re.match(ibrep, line), line) elif line.find("getelementptr ") != line.find("getelementptr ("): line = conv(re.match(normrep, line), line) sys.stdout.write(line) apply.sh: for name in "$@" do python3 `dirname "$0"`/update.py < "$name" > "$name.tmp" && mv "$name.tmp" "$name" rm -f "$name.tmp" done The actual commands: From llvm/src: find test/ -name *.ll | xargs ./apply.sh From llvm/src/tools/clang: find test/ -name *.mm -o -name *.m -o -name *.cpp -o -name *.c | xargs -I '{}' ../../apply.sh "{}" From llvm/src/tools/polly: find test/ -name *.ll | xargs ./apply.sh After that, check-all (with llvm, clang, clang-tools-extra, lld, compiler-rt, and polly all checked out). The extra 'rm' in the apply.sh script is due to a few files in clang's test suite using interesting unicode stuff that my python script was throwing exceptions on. None of those files needed to be migrated, so it seemed sufficient to ignore those cases. Reviewers: rafael, dexonsmith, grosser Differential Revision: http://reviews.llvm.org/D7636 llvm-svn: 230786
2015-02-28 03:29:02 +08:00
; CHECK: getelementptr inbounds [1 x i32], [1 x i32]* %p, i64 0, i64 0
[InstCombine] Remove unnecessary variable indexing into single-element arrays This change addresses a deficiency pointed out in PR22629. To copy from the bug report: [from the bug report] Consider this code: int f(int x) { int a[] = {12}; return a[x]; } GCC knows to optimize this to movl $12, %eax ret The code generated by recent Clang at -O3 is: movslq %edi, %rax movl .L_ZZ1fiE1a(,%rax,4), %eax retq .L_ZZ1fiE1a: .long 12 # 0xc [end from the bug report] This definitely seems worth fixing. I've also seen this kind of code before (as the base case of generic vector wrapper templates with one element). The general idea is to look at the GEP feeding a load or a store, which has some variable as its first non-zero index, and determine if that index must be zero (or else an out-of-bounds access would occur). We can do this for allocas and globals with constant initializers where we know the maximum size of the underlying object. When we find such a GEP, we create a new one for the memory access with that first variable index replaced with a constant zero. Even if we can't eliminate the memory access (and sometimes we can't), it is still useful because it removes unnecessary indexing calculations. llvm-svn: 229959
2015-02-20 11:05:53 +08:00
}
Fix a typo in rL265762 I accidentally replaced `mayBeOverridden` with `!isInterposable`. Remove the negation and add a test case that would've caught this. Many thanks to Håkan Hjort for spotting this! llvm-svn: 266551
2016-04-17 12:30:43 +08:00
define signext i32 @test4(i32 signext %x, i1 %y) #0 {
entry:
%idxprom = sext i32 %x to i64
%arrayidx = getelementptr inbounds [1 x i32], [1 x i32]* @f.c, i64 0, i64 %idxprom
%0 = load i32, i32* %arrayidx, align 4
ret i32 %0
; CHECK-LABEL: @test4
; CHECK: getelementptr inbounds [1 x i32], [1 x i32]* @f.c, i64 0, i64 %idxprom
}
[InstCombine] Remove unnecessary variable indexing into single-element arrays This change addresses a deficiency pointed out in PR22629. To copy from the bug report: [from the bug report] Consider this code: int f(int x) { int a[] = {12}; return a[x]; } GCC knows to optimize this to movl $12, %eax ret The code generated by recent Clang at -O3 is: movslq %edi, %rax movl .L_ZZ1fiE1a(,%rax,4), %eax retq .L_ZZ1fiE1a: .long 12 # 0xc [end from the bug report] This definitely seems worth fixing. I've also seen this kind of code before (as the base case of generic vector wrapper templates with one element). The general idea is to look at the GEP feeding a load or a store, which has some variable as its first non-zero index, and determine if that index must be zero (or else an out-of-bounds access would occur). We can do this for allocas and globals with constant initializers where we know the maximum size of the underlying object. When we find such a GEP, we create a new one for the memory access with that first variable index replaced with a constant zero. Even if we can't eliminate the memory access (and sometimes we can't), it is still useful because it removes unnecessary indexing calculations. llvm-svn: 229959
2015-02-20 11:05:53 +08:00
attributes #0 = { nounwind readnone }