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Check sign to detect overflow before changing compare stride.

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llvm-svn: 54710
This commit is contained in:
Devang Patel 2008-08-13 02:05:14 +00:00
parent 686068490f
commit a82e51a430
2 changed files with 39 additions and 1 deletions
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9
lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -1542,6 +1542,12 @@ ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
Value *NewIncV = NULL;
int64_t Scale = 1;
// Check stride constant and the comparision constant signs to detect
// overflow.
if (ICmpInst::isSignedPredicate(Predicate) &&
(CmpVal & SignBit) != (CmpSSInt & SignBit))
return Cond;
// Look for a suitable stride / iv as replacement.
std::stable_sort(StrideOrder.begin(), StrideOrder.end(), StrideCompare());
for (unsigned i = 0, e = StrideOrder.size(); i != e; ++i) {
@ -1640,11 +1646,12 @@ ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
// before the branch. See
// test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-*.ll
// for an example of this situation.
if (!Cond->hasOneUse())
if (!Cond->hasOneUse()) {
for (BasicBlock::iterator I = Cond, E = Cond->getParent()->end();
I != E; ++I)
if (I == NewIncV)
return Cond;
}
if (NewCmpVal != CmpVal) {
// Create a new compare instruction using new stride / iv.

31
test/Transforms/LoopStrengthReduce/2008-08-13-CmpStride.ll Normal file
View File

@ -0,0 +1,31 @@
; RUN: llvm-as < %s | opt -loop-reduce | llvm-dis | grep add | count 2
; PR 2662
@g_3 = common global i16 0 ; <i16*> [#uses=2]
@"\01LC" = internal constant [4 x i8] c"%d\0A\00" ; <[4 x i8]*> [#uses=1]
define void @func_1() nounwind {
entry:
br label %bb
bb: ; preds = %bb, %entry
%l_2.0.reg2mem.0 = phi i16 [ 0, %entry ], [ %t1, %bb ] ; <i16> [#uses=2]
%t0 = shl i16 %l_2.0.reg2mem.0, 1 ; <i16>:0 [#uses=1]
volatile store i16 %t0, i16* @g_3, align 2
%t1 = add i16 %l_2.0.reg2mem.0, -3 ; <i16>:1 [#uses=2]
%t2 = icmp slt i16 %t1, 1 ; <i1>:2 [#uses=1]
br i1 %t2, label %bb, label %return
return: ; preds = %bb
ret void
}
define i32 @main() nounwind {
entry:
tail call void @func_1( ) nounwind
volatile load i16* @g_3, align 2 ; <i16>:0 [#uses=1]
zext i16 %0 to i32 ; <i32>:1 [#uses=1]
tail call i32 (i8*, ...)* @printf( i8* getelementptr ([4 x i8]* @"\01LC", i32 0, i32 0), i32 %1 ) nounwind ; <i32>:2 [#uses=0]
ret i32 0
}
declare i32 @printf(i8*, ...) nounwind