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[InstCombine] add test and code comment to show potentially misguided icmp trunc transform 

llvm-svn: 285075
This commit is contained in:
Sanjay Patel 2016-10-25 15:16:39 +00:00
parent bd449c27d5
commit d59f7f9047
2 changed files with 16 additions and 0 deletions
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3
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1950,6 +1950,9 @@ Instruction *InstCombiner::foldICmpShlConstant(ICmpInst &Cmp,
And, Constant::getNullValue(And->getType()));
}
// FIXME: This transform can create illegal types. Use the DataLayout to
// decide when to try this?
// Transform (icmp pred iM (shl iM %v, N), C)
// -> (icmp pred i(M-N) (trunc %v iM to i(M-N)), (trunc (C>>N))
// Transform the shl to a trunc if (trunc (C>>N)) has no loss and M-N.

13
llvm/test/Transforms/InstCombine/icmp.ll
View File

@ -1208,6 +1208,19 @@ define i1 @icmp_shl16(i32 %x) {
ret i1 %cmp
}
; FIXME: We shouldn't be creating illegal types like i15 in InstCombine.
define i1 @icmp_shl17(i32 %x) {
; CHECK-LABEL: @icmp_shl17(
; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 %x to i15
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i15 [[TMP1]], 18
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl i32 %x, 17
%cmp = icmp slt i32 %shl, 2359296
ret i1 %cmp
}
define <2 x i1> @icmp_shl16_vec(<2 x i32> %x) {
; CHECK-LABEL: @icmp_shl16_vec(
; CHECK-NEXT: [[TMP1:%.*]] = trunc <2 x i32> %x to <2 x i16>