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An instruction in a loop is not guaranteed to be executed just because the loop

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has no exit blocks. Fixes PR12706!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155884 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2012-05-01 04:03:01 +00:00
parent 973f72a29a
commit 4056a73638
2 changed files with 27 additions and 0 deletions
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5
lib/Transforms/Scalar/LICM.cpp
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@ -618,6 +618,11 @@ bool LICM::isGuaranteedToExecute(Instruction &Inst) {
if (!DT->dominates(Inst.getParent(), ExitBlocks[i])) if (!DT->dominates(Inst.getParent(), ExitBlocks[i]))
return false; return false;
// As a degenerate case, if the loop is statically infinite then we haven't
// proven anything since there are no exit blocks.
if (ExitBlocks.empty())
return false;
return true; return true;
} }

22
test/Transforms/LICM/speculate.ll
View File

@ -165,3 +165,25 @@ for.inc: ; preds = %if.then, %for.body
for.end: ; preds = %for.inc, %entry for.end: ; preds = %for.inc, %entry
ret void ret void
} }
; SDiv is unsafe to speculate inside an infinite loop.
define void @unsafe_sdiv_c(i64 %a, i64 %b, i64* %p) {
entry:
; CHECK: entry:
; CHECK-NOT: sdiv
; CHECK: br label %for.body
br label %for.body
for.body:
%c = icmp eq i64 %b, 0
br i1 %c, label %backedge, label %if.then
if.then:
%d = sdiv i64 %a, %b
store i64 %d, i64* %p
br label %backedge
backedge:
br label %for.body
}