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[InstCombine] allow any pair of bitcasts to be combined

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This change is discussed in D15392 and should allow us to effectively
revert:
http://llvm.org/viewvc/llvm-project?view=revision&revision=255261
if we canonicalize bitcasts ahead of extracts.

It should be safe to convert any pair of bitcasts into a single bitcast, 
however, it was mentioned here:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20110829/127089.html
that we're not allowed to bitcast from an x86_mmx to some other types, but I'm 
not seeing any failures from that, and we have regression tests in CodeGen/X86
that appear to cover all of those cases. 

Some day we'll get to remove that MMX wart from LLVM IR completely?

Differential Revision: http://reviews.llvm.org/D15468



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255399 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel 2015-12-12 00:33:36 +00:00
parent 8f2bcca5c7
commit 63b29821f9
2 changed files with 17 additions and 21 deletions
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20
lib/IR/Instructions.cpp
View File

@ -2516,17 +2516,19 @@ unsigned CastInst::isEliminableCastPair(
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,13,12}, // AddrSpaceCast -+
};
// TODO: This logic could be encoded into the table above and handled in the
// switch below.
// If either of the casts are a bitcast from scalar to vector, disallow the
// merging. However, bitcast of A->B->A are allowed.
bool isFirstBitcast = (firstOp == Instruction::BitCast);
bool isSecondBitcast = (secondOp == Instruction::BitCast);
bool chainedBitcast = (SrcTy == DstTy && isFirstBitcast && isSecondBitcast);
// merging. However, any pair of bitcasts are allowed.
bool IsFirstBitcast = (firstOp == Instruction::BitCast);
bool IsSecondBitcast = (secondOp == Instruction::BitCast);
bool AreBothBitcasts = IsFirstBitcast && IsSecondBitcast;
// Check if any of the bitcasts convert scalars<->vectors.
if ((isFirstBitcast && isa<VectorType>(SrcTy) != isa<VectorType>(MidTy)) ||
(isSecondBitcast && isa<VectorType>(MidTy) != isa<VectorType>(DstTy)))
// Unless we are bitcasting to the original type, disallow optimizations.
if (!chainedBitcast) return 0;
// Check if any of the casts convert scalars <-> vectors.
if ((IsFirstBitcast && isa<VectorType>(SrcTy) != isa<VectorType>(MidTy)) ||
(IsSecondBitcast && isa<VectorType>(MidTy) != isa<VectorType>(DstTy)))
if (!AreBothBitcasts)
return 0;
int ElimCase = CastResults[firstOp-Instruction::CastOpsBegin]
[secondOp-Instruction::CastOpsBegin];

18
test/Transforms/InstCombine/bitcast-bitcast.ll
View File

@ -18,8 +18,7 @@ define <2 x i32> @bitcast_bitcast_s_s_v(i64 %a) {
ret <2 x i32> %bc2
; CHECK-LABEL: @bitcast_bitcast_s_s_v(
; CHECK-NEXT: %bc1 = bitcast i64 %a to double
; CHECK-NEXT: %bc2 = bitcast double %bc1 to <2 x i32>
; CHECK-NEXT: %bc2 = bitcast i64 %a to <2 x i32>
; CHECK-NEXT: ret <2 x i32> %bc2
}
@ -29,8 +28,7 @@ define double @bitcast_bitcast_s_v_s(i64 %a) {
ret double %bc2
; CHECK-LABEL: @bitcast_bitcast_s_v_s(
; CHECK-NEXT: %bc1 = bitcast i64 %a to <2 x i32>
; CHECK-NEXT: %bc2 = bitcast <2 x i32> %bc1 to double
; CHECK-NEXT: %bc2 = bitcast i64 %a to double
; CHECK-NEXT: ret double %bc2
}
@ -40,8 +38,7 @@ define <2 x i32> @bitcast_bitcast_s_v_v(i64 %a) {
ret <2 x i32> %bc2
; CHECK-LABEL: @bitcast_bitcast_s_v_v(
; CHECK-NEXT: %bc1 = bitcast i64 %a to <4 x i16>
; CHECK-NEXT: %bc2 = bitcast <4 x i16> %bc1 to <2 x i32>
; CHECK-NEXT: %bc2 = bitcast i64 %a to <2 x i32>
; CHECK-NEXT: ret <2 x i32> %bc2
}
@ -51,8 +48,7 @@ define i64 @bitcast_bitcast_v_s_s(<2 x i32> %a) {
ret i64 %bc2
; CHECK-LABEL: @bitcast_bitcast_v_s_s(
; CHECK-NEXT: %bc1 = bitcast <2 x i32> %a to double
; CHECK-NEXT: %bc2 = bitcast double %bc1 to i64
; CHECK-NEXT: %bc2 = bitcast <2 x i32> %a to i64
; CHECK-NEXT: ret i64 %bc2
}
@ -62,8 +58,7 @@ define <4 x i16> @bitcast_bitcast_v_s_v(<2 x i32> %a) {
ret <4 x i16> %bc2
; CHECK-LABEL: @bitcast_bitcast_v_s_v(
; CHECK-NEXT: %bc1 = bitcast <2 x i32> %a to double
; CHECK-NEXT: %bc2 = bitcast double %bc1 to <4 x i16>
; CHECK-NEXT: %bc2 = bitcast <2 x i32> %a to <4 x i16>
; CHECK-NEXT: ret <4 x i16> %bc2
}
@ -73,8 +68,7 @@ define double @bitcast_bitcast_v_v_s(<2 x float> %a) {
ret double %bc2
; CHECK-LABEL: @bitcast_bitcast_v_v_s(
; CHECK-NEXT: %bc1 = bitcast <2 x float> %a to <4 x i16>
; CHECK-NEXT: %bc2 = bitcast <4 x i16> %bc1 to double
; CHECK-NEXT: %bc2 = bitcast <2 x float> %a to double
; CHECK-NEXT: ret double %bc2
}