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[SCEV] Properly guard reasoning about infinite loops being UB on mustprogress

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Noticed via code inspection. We changed the semantics of the IR when we added mustprogress, and we appear to have not updated this location.

Differential Revision: https://reviews.llvm.org/D103834
This commit is contained in:
Philip Reames 2021-06-07 14:46:57 -07:00
parent 29a047ef9b
commit db2ffb1268
3 changed files with 27 additions and 6 deletions
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2
lib/Analysis/ScalarEvolution.cpp
View File

@ -11470,7 +11470,7 @@ ScalarEvolution::howManyLessThans(const SCEV *LHS, const SCEV *RHS,
// A[i] = i;
//
if (PredicatedIV || !NoWrap || isKnownNonPositive(Stride) ||
!loopHasNoSideEffects(L))
!loopIsFiniteByAssumption(L))
return getCouldNotCompute();
} else if (!Stride->isOne() && !NoWrap) {
auto isUBOnWrap = [&]() {

29
test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll
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@ -13,8 +13,7 @@
target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
; Function Attrs: norecurse nounwind
define void @foo1(i32* nocapture %A, i32 %n, i32 %s) #0 {
define void @foo1(i32* nocapture %A, i32 %n, i32 %s) mustprogress {
entry:
%cmp4 = icmp sgt i32 %n, 0
br i1 %cmp4, label %for.body, label %for.end
@ -42,8 +41,7 @@ for.end: ; preds = %for.body, %entry
; loops with unknown stride.
; CHECK: max backedge-taken count is -1
; Function Attrs: norecurse nounwind
define void @foo2(i32* nocapture %A, i32 %n, i32 %s) #0 {
define void @foo2(i32* nocapture %A, i32 %n, i32 %s) mustprogress {
entry:
br label %for.body
@ -61,3 +59,26 @@ for.end: ; preds = %for.body, %entry
ret void
}
; Check that without mustprogress we don't make assumptions about infinite
; loops being UB.
; CHECK: Determining loop execution counts for: @foo3
; CHECK: Loop %for.body: Unpredictable backedge-taken count.
; CHECK: Loop %for.body: Unpredictable max backedge-taken count.
define void @foo3(i32* nocapture %A, i32 %n, i32 %s) {
entry:
br label %for.body
for.body: ; preds = %entry, %for.body
%i.05 = phi i32 [ %add, %for.body ], [ 0, %entry ]
%arrayidx = getelementptr inbounds i32, i32* %A, i32 %i.05
%0 = load i32, i32* %arrayidx, align 4
%inc = add nsw i32 %0, 1
store i32 %inc, i32* %arrayidx, align 4
%add = add nsw i32 %i.05, %s
%cmp = icmp slt i32 %add, %n
br i1 %cmp, label %for.body, label %for.end
for.end: ; preds = %for.body, %entry
ret void
}

2
test/Transforms/LoopVectorize/pr38697.ll
View File

@ -30,7 +30,7 @@ target triple = "x86_64-unknown-linux-gnu"
; Verify that a 'udiv' does not appear in the 'loop1.preheader' block, and that
; a 'udiv' has been inserted at the top of the 'while.body.preheader' block.
define void @testCountIncrLoop(i8* %ptr, i32 %lim, i32 %count, i32 %val) {
define void @testCountIncrLoop(i8* %ptr, i32 %lim, i32 %count, i32 %val) mustprogress {
; CHECK-LABEL: @testCountIncrLoop(
; CHECK-NEXT: entry:
; CHECK: loop1.preheader: