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[SLSR] garbage-collect unused instructions 

Summary:
After we rewrite a candidate, the instructions used by the old form may
become unused. This patch cleans up these unused instructions so that we
needn't run DCE after SLSR.

Test Plan: removed -dce in all the SLSR tests

Reviewers: broune, meheff

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9101

llvm-svn: 235410
This commit is contained in:
Jingyue Wu 2015-04-21 19:56:18 +00:00
parent f763c3fd45
commit f1edf3e88f
5 changed files with 17 additions and 7 deletions
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16
llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
View File

@ -68,6 +68,7 @@
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
using namespace PatternMatch;
@ -599,9 +600,14 @@ void StraightLineStrengthReduce::rewriteCandidateWithBasis(
switch (C.CandidateKind) {
case Candidate::Add:
case Candidate::Mul:
// C = Basis + Bump
if (BinaryOperator::isNeg(Bump)) {
// If Bump is a neg instruction, emit C = Basis - (-Bump).
Reduced =
Builder.CreateSub(Basis.Ins, BinaryOperator::getNegArgument(Bump));
// We only use the negative argument of Bump, and Bump itself may be
// trivially dead.
RecursivelyDeleteTriviallyDeadInstructions(Bump);
} else {
Reduced = Builder.CreateAdd(Basis.Ins, Bump);
}
@ -637,7 +643,6 @@ void StraightLineStrengthReduce::rewriteCandidateWithBasis(
};
Reduced->takeName(C.Ins);
C.Ins->replaceAllUsesWith(Reduced);
C.Ins->dropAllReferences();
// Unlink C.Ins so that we can skip other candidates also corresponding to
// C.Ins. The actual deletion is postponed to the end of runOnFunction.
C.Ins->removeFromParent();
@ -670,8 +675,13 @@ bool StraightLineStrengthReduce::runOnFunction(Function &F) {
}
// Delete all unlink instructions.
for (auto I : UnlinkedInstructions) {
delete I;
for (auto *UnlinkedInst : UnlinkedInstructions) {
for (unsigned I = 0, E = UnlinkedInst->getNumOperands(); I != E; ++I) {
Value *Op = UnlinkedInst->getOperand(I);
UnlinkedInst->setOperand(I, nullptr);
RecursivelyDeleteTriviallyDeadInstructions(Op);
}
delete UnlinkedInst;
}
bool Ret = !UnlinkedInstructions.empty();
UnlinkedInstructions.clear();

2
llvm/test/Transforms/StraightLineStrengthReduce/X86/no-slsr.ll
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@ -1,4 +1,4 @@
; RUN: opt < %s -slsr -gvn -dce -S | FileCheck %s
; RUN: opt < %s -slsr -gvn -S | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

2
llvm/test/Transforms/StraightLineStrengthReduce/slsr-add.ll
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@ -1,4 +1,4 @@
; RUN: opt < %s -slsr -gvn -dce -S | FileCheck %s
; RUN: opt < %s -slsr -gvn -S | FileCheck %s
target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"

2
llvm/test/Transforms/StraightLineStrengthReduce/slsr-gep.ll
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@ -1,4 +1,4 @@
; RUN: opt < %s -slsr -gvn -dce -S | FileCheck %s
; RUN: opt < %s -slsr -gvn -S | FileCheck %s
target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"

2
llvm/test/Transforms/StraightLineStrengthReduce/slsr-mul.ll
View File

@ -1,4 +1,4 @@
; RUN: opt < %s -slsr -gvn -dce -S | FileCheck %s
; RUN: opt < %s -slsr -gvn -S | FileCheck %s
target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"