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[MergeICmp] We can discard initial blocks that do other work 

Summary:
 We can discard initial blocks that do other work
We do not need to limit ourselves to just the first block in the chain.

Reviewers: courbet, davide

Reviewed By: courbet

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D44029

llvm-svn: 326698
This commit is contained in:
Xin Tong 2018-03-05 13:54:47 +00:00
parent b3748f71df
commit 8345c0e3a5
2 changed files with 72 additions and 3 deletions
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11
llvm/lib/Transforms/Scalar/MergeICmps.cpp
View File

@ -291,8 +291,8 @@ BCECmpChain::BCECmpChain(const std::vector<BasicBlock *> &Blocks, PHINode &Phi)
if (Comparison.doesOtherWork()) {
DEBUG(dbgs() << "block '" << Comparison.BB->getName()
<< "' does extra work besides compare\n");
if (BlockIdx == 0) { // First block.
// TODO(courbet): The first block can do other things, and we should
if (Comparisons.empty()) {
// TODO(courbet): The initial block can do other things, and we should
// split them apart in a separate block before the comparison chain.
// Right now we just discard it and make the chain shorter.
DEBUG(dbgs()
@ -333,7 +333,12 @@ BCECmpChain::BCECmpChain(const std::vector<BasicBlock *> &Blocks, PHINode &Phi)
DEBUG(dbgs() << "\n");
Comparisons.push_back(Comparison);
}
assert(!Comparisons.empty() && "chain with no BCE basic blocks");
// It is possible we have no suitable comparison to merge.
if (Comparisons.empty()) {
DEBUG(dbgs() << "chain with no BCE basic blocks, no merge\n");
return;
}
EntryBlock_ = Comparisons[0].BB;
Comparisons_ = std::move(Comparisons);
#ifdef MERGEICMPS_DOT_ON

64
llvm/test/Transforms/MergeICmps/X86/multiple-blocks-does-work.ll Normal file
View File

@ -0,0 +1,64 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -mergeicmps -mtriple=x86_64-unknown-unknown -S | FileCheck %s --check-prefix=X86
%"struct.std::pair" = type { i32, i32, i32, i32 }
declare void @foo(...)
; We can discard %entry and %land.rhs.i, but still merge the last 2 blocks.
define zeroext i1 @opeq1(
; X86-LABEL: @opeq1(
; X86: land.rhs.i.2:
; X86-NEXT: [[THIRD_I:%.*]] = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* [[A:%.*]], i64 0, i32 2
; X86-NEXT: [[THIRD1_I:%.*]] = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* [[B:%.*]], i64 0, i32 2
; X86-NEXT: [[CSTR:%.*]] = bitcast i32* [[THIRD_I]] to i8*
; X86-NEXT: [[CSTR1:%.*]] = bitcast i32* [[THIRD1_I]] to i8*
; X86-NEXT: [[MEMCMP:%.*]] = call i32 @memcmp(i8* [[CSTR]], i8* [[CSTR1]], i64 8)
; X86-NEXT: [[TMP0:%.*]] = icmp eq i32 [[MEMCMP]], 0
; X86-NEXT: br label [[OPEQ1_EXIT:%.*]]
; X86: opeq1.exit:
; X86-NEXT: [[TMP1:%.*]] = phi i1 [ false, %entry ], [ false, %land.rhs.i ], [ [[TMP0]], %land.rhs.i.2 ]
; X86-NEXT: ret i1 [[TMP1]]
;
%"struct.std::pair"* nocapture readonly dereferenceable(16) %a,
%"struct.std::pair"* nocapture readonly dereferenceable(16) %b) local_unnamed_addr #0 {
entry:
%first.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 0
%0 = load i32, i32* %first.i, align 4
%first1.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 0
%1 = load i32, i32* %first1.i, align 4
; Does other work.
call void (...) @foo()
%cmp.i = icmp eq i32 %0, %1
br i1 %cmp.i, label %land.rhs.i, label %opeq1.exit
land.rhs.i:
%second.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 1
%2 = load i32, i32* %second.i, align 4
%second2.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 1
%3 = load i32, i32* %second2.i, align 4
; Does other work.
call void (...) @foo()
%cmp2.i = icmp eq i32 %2, %3
br i1 %cmp2.i, label %land.rhs.i.2, label %opeq1.exit
land.rhs.i.2:
%third.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 2
%4 = load i32, i32* %third.i, align 4
%third2.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 2
%5 = load i32, i32* %third2.i, align 4
%cmp3.i = icmp eq i32 %4, %5
br i1 %cmp3.i, label %land.rhs.i.3, label %opeq1.exit
land.rhs.i.3:
%fourth.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 3
%6 = load i32, i32* %fourth.i, align 4
%fourth2.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 3
%7 = load i32, i32* %fourth2.i, align 4
%cmp4.i = icmp eq i32 %6, %7
br label %opeq1.exit
opeq1.exit:
%8 = phi i1 [ false, %entry ], [ false, %land.rhs.i] , [ false, %land.rhs.i.2 ], [ %cmp4.i, %land.rhs.i.3 ]
ret i1 %8
}