[llvm] r186152 - Revert "indvars: Improve LFTR by eliminating truncation when comparing
Chandler Carruth
chandlerc at gmail.com
Fri Jul 12 04:18:55 PDT 2013
Author: chandlerc
Date: Fri Jul 12 06:18:55 2013
New Revision: 186152
URL: http://llvm.org/viewvc/llvm-project?rev=186152&view=rev
Log:
Revert "indvars: Improve LFTR by eliminating truncation when comparing
against a constant."
This reverts commit r186107. It didn't handle wrapping arithmetic in the
loop correctly and thus caused the following C program to count from
0 to UINT64_MAX instead of from 0 to 255 as intended:
#include <stdio.h>
int main() {
unsigned char first = 0, last = 255;
do { printf("%d\n", first); } while (first++ != last);
}
Full test case and instructions to reproduce with just the -indvars pass
sent to the original review thread rather than to r186107's commit.
Removed:
llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=186152&r1=186151&r2=186152&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Fri Jul 12 06:18:55 2013
@@ -1612,29 +1612,10 @@ LinearFunctionTestReplace(Loop *L,
<< " IVCount:\t" << *IVCount << "\n");
IRBuilder<> Builder(BI);
-
- unsigned CmpIndVarSize = SE->getTypeSizeInBits(CmpIndVar->getType());
- unsigned ExitCntSize = SE->getTypeSizeInBits(ExitCnt->getType());
- if (CmpIndVarSize > ExitCntSize) {
- const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
- const SCEV *ARStart = AR->getStart();
- const SCEV *ARStep = AR->getStepRecurrence(*SE);
- if (isa<SCEVConstant>(ARStart) && isa<SCEVConstant>(IVCount)) {
- const APInt &Start = cast<SCEVConstant>(ARStart)->getValue()->getValue();
- const APInt &Count = cast<SCEVConstant>(IVCount)->getValue()->getValue();
-
- APInt NewLimit;
- if (cast<SCEVConstant>(ARStep)->getValue()->isNegative())
- NewLimit = Start - Count.zext(CmpIndVarSize);
- else
- NewLimit = Start + Count.zext(CmpIndVarSize);
- ExitCnt = ConstantInt::get(CmpIndVar->getType(), NewLimit);
-
- DEBUG(dbgs() << " Widen RHS:\t" << *ExitCnt << "\n");
- } else {
- CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
- "lftr.wideiv");
- }
+ if (SE->getTypeSizeInBits(CmpIndVar->getType())
+ > SE->getTypeSizeInBits(ExitCnt->getType())) {
+ CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
+ "lftr.wideiv");
}
Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond");
Removed: llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll?rev=186151&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll (original)
+++ llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll (removed)
@@ -1,25 +0,0 @@
-;RUN: opt -S %s -indvars | FileCheck %s
-
-; Function Attrs: nounwind uwtable
-define void @foo() #0 {
-entry:
- br label %for.body
-
-for.body: ; preds = %entry, %for.body
- %i.01 = phi i16 [ 0, %entry ], [ %inc, %for.body ]
- %conv2 = sext i16 %i.01 to i32
- call void @bar(i32 %conv2) #1
- %inc = add i16 %i.01, 1
-;CHECK-NOT: %lftr.wideiv = trunc i32 %indvars.iv.next to i16
-;CHECK: %exitcond = icmp ne i32 %indvars.iv.next, 512
- %cmp = icmp slt i16 %inc, 512
- br i1 %cmp, label %for.body, label %for.end
-
-for.end: ; preds = %for.body
- ret void
-}
-
-declare void @bar(i32)
-
-attributes #0 = { nounwind uwtable }
-attributes #1 = { nounwind }
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