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Add argmononly attribute to strlen and wcslen, i.e. they only read memory (string) passed to them. 

Summary:
This allows strlen to be moved out of the loop in case its argument is
not modified in the loop in LICM.

Reviewers: hfinkel, davide, sanjoy, dberlin

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D34323

llvm-svn: 305641
This commit is contained in:
Xin Tong 2017-06-18 03:10:26 +00:00
parent 90e4c3f357
commit 9d2a5b1cf7
3 changed files with 24 additions and 3 deletions
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1
llvm/lib/Transforms/Utils/BuildLibCalls.cpp
View File

@ -116,6 +116,7 @@ bool llvm::inferLibFuncAttributes(Function &F, const TargetLibraryInfo &TLI) {
case LibFunc_wcslen:
Changed |= setOnlyReadsMemory(F);
Changed |= setDoesNotThrow(F);
Changed |= setOnlyAccessesArgMemory(F);
Changed |= setDoesNotCapture(F, 0);
return Changed;
case LibFunc_strchr:

7
llvm/test/Transforms/InferFunctionAttrs/annotate.ll
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@ -844,7 +844,7 @@ declare i64 @strcspn(i8*, i8*)
; CHECK: declare noalias i8* @strdup(i8* nocapture readonly) [[G0]]
declare i8* @strdup(i8*)
; CHECK: declare i64 @strlen(i8* nocapture) [[G1]]
; CHECK: declare i64 @strlen(i8* nocapture) [[G2:#[0-9]+]]
declare i64 @strlen(i8*)
; CHECK: declare i32 @strncasecmp(i8* nocapture, i8* nocapture, i64) [[G1]]
@ -996,10 +996,11 @@ declare i64 @write(i32, i8*, i64)
; memset_pattern16 isn't available everywhere.
; CHECK-DARWIN: declare void @memset_pattern16(i8* nocapture, i8* nocapture readonly, i64) [[G2:#[0-9]+]]
; CHECK-DARWIN: declare void @memset_pattern16(i8* nocapture, i8* nocapture readonly, i64) [[G3:#[0-9]+]]
declare void @memset_pattern16(i8*, i8*, i64)
; CHECK: attributes [[G0]] = { nounwind }
; CHECK: attributes [[G1]] = { nounwind readonly }
; CHECK-DARWIN: attributes [[G2]] = { argmemonly }
; CHECK: attributes [[G2]] = { argmemonly nounwind readonly }
; CHECK-DARWIN: attributes [[G3]] = { argmemonly }

19
llvm/test/Transforms/LICM/strlen.ll Normal file
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@ -0,0 +1,19 @@
; RUN: opt -S -inferattrs -basicaa -licm < %s | FileCheck %s
define void @test(i64* noalias %loc, i8* noalias %a) {
; CHECK-LABEL: @test
; CHECK: @strlen
; CHECK-LABEL: loop:
br label %loop
loop:
%res = call i64 @strlen(i8* %a)
store i64 %res, i64* %loc
br label %loop
}
; CHECK: declare i64 @strlen(i8* nocapture) #0
; CHECK: attributes #0 = { argmemonly nounwind readonly }
declare i64 @strlen(i8*)