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[ConstantFold] Don't try to strip fp -> int bitcasts to simplify icmps

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ConstantFold has logic to take icmp (bitcast x to y), null and strip the
bitcast. This makes sense in general, but not if x has floating-point type. In
this case, we'd need a fcmp, not an icmp, and the code will assert. We normally
don't see this situation because we constant fold fp -> int bitcasts, however,
we'll see it for bitcasts of ppc_fp128 -> i128. This is because that bitcast is
Endian-dependent, and as a result, we don't simplify it in ConstantFold (we
could, but no one has yet added the necessary logic). Regardless, ConstantFold
should not depend on that canonicalization for correctness.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268534 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel 2016-05-04 19:37:08 +00:00
parent 128ff37f5e
commit 5813ee1a22
2 changed files with 56 additions and 0 deletions
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4
lib/IR/ConstantFold.cpp
View File

@ -1529,6 +1529,10 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
case Instruction::BitCast:
case Instruction::ZExt:
case Instruction::SExt:
// We can't evaluate floating point casts or truncations.
if (CE1Op0->getType()->isFloatingPointTy())
break;
// If the cast is not actually changing bits, and the second operand is a
// null pointer, do the comparison with the pre-casted value.
if (V2->isNullValue() &&

52
test/Transforms/IPConstantProp/fp-bc-icmp-const-fold.ll Normal file
View File

@ -0,0 +1,52 @@
; RUN: opt -S -ipsccp < %s | FileCheck %s
target datalayout = "E-m:e-i64:64-n32:64"
target triple = "powerpc64-bgq-linux"
define void @test(i32 signext %n) {
; CHECK-LABEL: @test
entry:
br i1 undef, label %if.then, label %if.end
if.then: ; preds = %entry
ret void
if.end: ; preds = %entry
br i1 undef, label %if.then2, label %if.end4
if.then2: ; preds = %if.end
unreachable
if.end4: ; preds = %if.end
%sub.n = select i1 undef, i32 undef, i32 %n
switch i32 %sub.n, label %if.else14 [
i32 0, label %if.then9
i32 1, label %if.then12
]
if.then9: ; preds = %if.end4
unreachable
if.then12: ; preds = %if.end4
unreachable
if.else14: ; preds = %if.end4
br label %do.body
do.body: ; preds = %do.body, %if.else14
%scale.0 = phi ppc_fp128 [ 0xM3FF00000000000000000000000000000, %if.else14 ], [ %scale.0, %do.body ]
br i1 undef, label %do.body, label %if.then33
if.then33: ; preds = %do.body
br i1 undef, label %_ZN5boost4math4signIgEEiRKT_.exit30, label %cond.false.i28
cond.false.i28: ; preds = %if.then33
%0 = bitcast ppc_fp128 %scale.0 to i128
%tobool.i26 = icmp slt i128 %0, 0
br label %_ZN5boost4math4signIgEEiRKT_.exit30
_ZN5boost4math4signIgEEiRKT_.exit30: ; preds = %cond.false.i28, %if.then33
unreachable
}