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[indvars] Fix pr52276 (missing one use check) 

The recently added logic to canonicalize exit conditions to unsigned relies on facts which hold about the use (i.e. exit test).  Applying this blindly to the icmp is not legal, as there may be another use which never reaches the exit.  Restrict ourselves to case where we have a single use.
This commit is contained in:
Philip Reames 2021-10-25 09:25:00 -07:00
parent f41d08540b
commit f82cf6187f
2 changed files with 58 additions and 1 deletions
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2
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
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@ -1430,7 +1430,7 @@ bool IndVarSimplify::canonicalizeExitCondition(Loop *L) {
assert(BI->isConditional() && "exit branch must be conditional");
auto *ICmp = dyn_cast<ICmpInst>(BI->getCondition());
if (!ICmp)
if (!ICmp || !ICmp->hasOneUse())
continue;
auto *LHS = ICmp->getOperand(0);

57
llvm/test/Transforms/IndVarSimplify/finite-exit-comparisons.ll
View File

@ -154,6 +154,63 @@ for.end: ; preds = %for.body, %entry
ret void
}
; Fact holds for exiting branch, but not for earlier use
; We could recognize the unreachable loop here, but don't currently. Its
; also not terribly interesting, because EarlyCSE will fold condition.
define void @slt_neg_multiple_use(i8 %start) mustprogress {
; CHECK-LABEL: @slt_neg_multiple_use(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[ZEXT:%.*]] = zext i8 [[START:%.*]] to i16
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i16 [[ZEXT]], 254
; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY_PREHEADER:%.*]], label [[FOR_END:%.*]]
; CHECK: for.body.preheader:
; CHECK-NEXT: br label [[FOR_BODY:%.*]]
; CHECK: for.body:
; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END_LOOPEXIT:%.*]]
; CHECK: for.end.loopexit:
; CHECK-NEXT: br label [[FOR_END]]
; CHECK: for.end:
; CHECK-NEXT: ret void
;
entry:
%zext = zext i8 %start to i16
%cmp = icmp slt i16 %zext, 254
br i1 %cmp, label %for.body, label %for.end
for.body: ; preds = %entry, %for.body
br i1 %cmp, label %for.body, label %for.end
for.end: ; preds = %for.body, %entry
ret void
}
define void @slt_neg_multiple_use2(i8 %start, i16 %n) mustprogress {
; CHECK-LABEL: @slt_neg_multiple_use2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[ZEXT:%.*]] = zext i8 [[START:%.*]] to i16
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i16 [[ZEXT]], [[N:%.*]]
; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY_PREHEADER:%.*]], label [[FOR_END:%.*]]
; CHECK: for.body.preheader:
; CHECK-NEXT: br label [[FOR_BODY:%.*]]
; CHECK: for.body:
; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END_LOOPEXIT:%.*]]
; CHECK: for.end.loopexit:
; CHECK-NEXT: br label [[FOR_END]]
; CHECK: for.end:
; CHECK-NEXT: ret void
;
entry:
%zext = zext i8 %start to i16
%cmp = icmp slt i16 %zext, %n
br i1 %cmp, label %for.body, label %for.end
for.body: ; preds = %entry, %for.body
br i1 %cmp, label %for.body, label %for.end
for.end: ; preds = %for.body, %entry
ret void
}
@G = external global i8
; Negative case where the loop could be infinite and make progress