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Add a missing safety check to ProcessUGT_ADDCST_ADD. Fixes PR11438.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145316 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2011-11-28 23:32:19 +00:00
parent 4544da484d
commit 54b92113e2
2 changed files with 30 additions and 0 deletions
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8
lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -1657,6 +1657,14 @@ static Instruction *ProcessUGT_ADDCST_ADD(ICmpInst &I, Value *A, Value *B,
CI1->getValue() != APInt::getLowBitsSet(CI1->getBitWidth(), NewWidth)) CI1->getValue() != APInt::getLowBitsSet(CI1->getBitWidth(), NewWidth))
return 0; return 0;
// This is only really a signed overflow check if the inputs have been
// sign-extended; check for that condition. For example, if CI2 is 2^31 and
// the operands of the add are 64 bits wide, we need at least 33 sign bits.
unsigned NeededSignBits = CI1->getBitWidth() - NewWidth + 1;
if (IC.ComputeNumSignBits(A) < NeededSignBits ||
IC.ComputeNumSignBits(B) < NeededSignBits)
return 0;
// In order to replace the original add with a narrower // In order to replace the original add with a narrower
// llvm.sadd.with.overflow, the only uses allowed are the add-with-constant // llvm.sadd.with.overflow, the only uses allowed are the add-with-constant
// and truncates that discard the high bits of the add. Verify that this is // and truncates that discard the high bits of the add. Verify that this is

22
test/Transforms/InstCombine/overflow.ll
View File

@ -130,4 +130,26 @@ entry:
ret i64 %Q ret i64 %Q
} }
; CHECK: @test8
; PR11438
; This is @test1, but the operands are not sign-extended. Make sure
; we don't transform this case.
define i32 @test8(i64 %a, i64 %b) nounwind ssp {
entry:
; CHECK-NOT: llvm.sadd
; CHECK: add i64 %a, %b
; CHECK-NOT: llvm.sadd
; CHECK: ret
%add = add i64 %a, %b
%add.off = add i64 %add, 2147483648
%0 = icmp ugt i64 %add.off, 4294967295
br i1 %0, label %if.then, label %if.end
if.then:
tail call void @throwAnExceptionOrWhatever() nounwind
br label %if.end
if.end:
%conv9 = trunc i64 %add to i32
ret i32 %conv9
}