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[InstCombine] limit icmp transform to ConstantInt (PR28011)

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In r271810 ( http://reviews.llvm.org/rL271810 ), I loosened the check
above this to work for any Constant rather than ConstantInt. AFAICT, 
that part makes sense if we can determine that the shrunken/extended 
constant remained equal. But it doesn't make sense for this later 
transform where we assume that the constant DID change. 

This could assert for a ConstantExpr:
https://llvm.org/bugs/show_bug.cgi?id=28011

And it could be wrong for a vector as shown in the added regression test.

llvm-svn: 271908
This commit is contained in:
Sanjay Patel 2016-06-06 16:56:57 +00:00
parent 810d7e88a4
commit 6ec19288fa
2 changed files with 33 additions and 3 deletions
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8
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2459,12 +2459,14 @@ Instruction *InstCombiner::visitICmpInstWithCastAndCast(ICmpInst &ICmp) {
return new ICmpInst(ICmp.getUnsignedPredicate(), LHSCIOp, Res1);
}
// The re-extended constant changed so the constant cannot be represented
// in the shorter type. Consequently, we cannot emit a simple comparison.
// The re-extended constant changed, partly changed (in the case of a vector),
// or could not be determined to be equal (in the case of a constant
// expression), so the constant cannot be represented in the shorter type.
// Consequently, we cannot emit a simple comparison.
// All the cases that fold to true or false will have already been handled
// by SimplifyICmpInst, so only deal with the tricky case.
if (isSignedCmp || !isSignedExt)
if (isSignedCmp || !isSignedExt || !isa<ConstantInt>(C))
return nullptr;
// Evaluate the comparison for LT (we invert for GT below). LE and GE cases

28
test/Transforms/InstCombine/2004-11-27-SetCCForCastLargerAndConstant.ll
View File

@ -22,6 +22,34 @@ define i1 @lt_signed_to_large_unsigned(i8 %SB) {
ret i1 %C
}
; PR28011 - https://llvm.org/bugs/show_bug.cgi?id=28011
; The above transform only applies to scalar integers; it shouldn't be attempted for constant expressions or vectors.
@a = common global i32** null
@b = common global [1 x i32] zeroinitializer
define i1 @PR28011(i16 %a) {
; CHECK-LABEL: @PR28011(
; CHECK-NEXT: [[CONV:%.*]] = sext i16 %a to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp ne i32 [[CONV]], or (i32 zext (i1 icmp ne (i32*** bitcast ([1 x i32]* @b to i32***), i32*** @a) to i32), i32 1)
; CHECK-NEXT: ret i1 [[CMP]]
;
%conv = sext i16 %a to i32
%cmp = icmp ne i32 %conv, or (i32 zext (i1 icmp ne (i32*** bitcast ([1 x i32]* @b to i32***), i32*** @a) to i32), i32 1)
ret i1 %cmp
}
define <2 x i1> @lt_signed_to_large_unsigned_vec(<2 x i8> %SB) {
; CHECK-LABEL: @lt_signed_to_large_unsigned_vec(
; CHECK-NEXT: [[Y:%.*]] = sext <2 x i8> %SB to <2 x i32>
; CHECK-NEXT: [[C:%.*]] = icmp ult <2 x i32> [[Y]], <i32 1024, i32 2>
; CHECK-NEXT: ret <2 x i1> [[C]]
;
%Y = sext <2 x i8> %SB to <2 x i32>
%C = icmp ult <2 x i32> %Y, <i32 1024, i32 2>
ret <2 x i1> %C
}
define i1 @lt_signed_to_large_signed(i8 %SB) {
; CHECK-LABEL: @lt_signed_to_large_signed(
; CHECK-NEXT: ret i1 true