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InstCombine: fold (sitofp (zext x)) to (uitofp x)

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This is okay because the zext guarantees the high bit is zero,
and so the value is unsigned.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235364 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Fiona Glaser 2015-04-21 00:05:41 +00:00
parent 1aebbfac0a
commit b5750565de
2 changed files with 13 additions and 1 deletions
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5
lib/IR/Instructions.cpp
View File

@ -2118,7 +2118,7 @@ unsigned CastInst::isEliminableCastPair(
// N X X U S F F N X N 2 V V |
// C T T I I P P C T T P T T -+
{ 1, 0, 0,99,99, 0, 0,99,99,99, 0, 3, 0}, // Trunc -+
{ 8, 1, 9,99,99, 2, 0,99,99,99, 2, 3, 0}, // ZExt |
{ 8, 1, 9,99,99, 2,17,99,99,99, 2, 3, 0}, // ZExt |
{ 8, 0, 1,99,99, 0, 2,99,99,99, 0, 3, 0}, // SExt |
{ 0, 0, 0,99,99, 0, 0,99,99,99, 0, 3, 0}, // FPToUI |
{ 0, 0, 0,99,99, 0, 0,99,99,99, 0, 3, 0}, // FPToSI |
@ -2285,6 +2285,9 @@ unsigned CastInst::isEliminableCastPair(
"Illegal bitcast, ptrtoint sequence!");
// Allowed, use second cast's opcode
return secondOp;
case 17:
// (sitofp (zext x)) -> (uitofp x)
return Instruction::UIToFP;
case 99:
// Cast combination can't happen (error in input). This is for all cases
// where the MidTy is not the same for the two cast instructions.

9
test/Transforms/InstCombine/cast.ll
View File

@ -1104,3 +1104,12 @@ define i32 @PR21388(i32* %v) {
; CHECK-NEXT: %[[sext:.*]] = sext i1 %[[icmp]] to i32
; CHECK-NEXT: ret i32 %[[sext]]
}
define float @sitofp_zext(i16 %a) {
; CHECK-LABEL: @sitofp_zext(
; CHECK-NEXT: %[[sitofp:.*]] = uitofp i16 %a to float
; CHECK-NEXT: ret float %[[sitofp]]
%zext = zext i16 %a to i32
%sitofp = sitofp i32 %zext to float
ret float %sitofp
}