[FastISel][X86] Teach how to select SSE2/AVX bitcasts between 128/256-bit vector types.

[andreadb]

Summary

While looking at the -O0 codegen, I noticed that X86FastIsel doesn't know how to fast select bitcasts between 128-bit vetor types.

This patch is a (very) minor FastISel improvement.
It teaches FastISel the following two things:

1. On SSE2, no instructions are needed for bitcasts between 128-bit vector types.
2. On AVX, no instructions are needed for bitcasts between 256-bit vector types.

Example:

%1 = bitcast <4 x i32> %V to <2 x i64>

Before (-fast-isel -fast-isel-abort=1):

FastIsel miss:  %1 = bitcast <4 x i32> %V to <2 x i64>

Now we don't fall back to SelectionDAG and we correctly fold that computation propagating the register associated to %V.

Please let me know if okay to submit.

Thanks,
Andrea

[qcolombet]

Hi Andrea,

Couple of questions, see inline, otherwise looks quite reasonable to me.

Thanks,
-Quentin

lib/Target/X86/X86FastISel.cpp

3240 ↗

(On Diff #36242)

Why do we have to check that here?
We are interested in 128 and 256 bit vector types. I do not understand why the fact that f64 may be mapped on x87 need to be considered?

3247 ↗

(On Diff #36242)

Could you add test cases for these checks?
In particular the different SizeInBits part.

[andreadb]

Hi Quentin,

lib/Target/X86/X86FastISel.cpp

3240 ↗

(On Diff #36242)

While it is true that X86ScalarSSEf64 is initialized to Subtarget->hasSSE2(), X86ScalarSSEf64 should only be used to reason on f64 types. So it is wrong to use it in this context.

I will change it to an explicit check for feature SSE2.

3247 ↗

(On Diff #36242)

My bad.. That check makes no sense since source and destination bit widths must always be identical for bitcast operations.
I will remove that redundant check.

[qcolombet]

lib/Target/X86/X86FastISel.cpp

3247 ↗

(On Diff #36242)

Hehe, thanks for checking, I was wondering if the data layout may break that assumption and if it does, when!

[andreadb]

Patch Updated.

Replaced the check for X86ScalarSSEf64 with a more appropriate check for SSE2.
Removed redundant check for type sizes.

Please let me know if okay to commit.
Thanks!

[qcolombet]

Thanks Andrea!

LGTM.

Cheers,
-Quentin

llvm/trunk/lib/Target/X86/X86FastISel.cpp

if (DstVT.bitsGT(SrcVT))
       return X86SelectZExt(I);
     if (DstVT.bitsLT(SrcVT))
       return X86SelectTrunc(I);
     unsigned Reg = getRegForValue(I->getOperand(0));
     if (Reg == 0) return false;
     updateValueMap(I, Reg);
     return true;
   }
+  case Instruction::BitCast: {
+    // Select SSE2/AVX bitcasts between 128/256 bit vector types.
+    if (!Subtarget->hasSSE2())
+      return false;
+
+    EVT SrcVT = TLI.getValueType(DL, I->getOperand(0)->getType());
+    EVT DstVT = TLI.getValueType(DL, I->getType());
+
+    if (!SrcVT.isSimple() || !DstVT.isSimple())
+      return false;
+
+    if (!SrcVT.is128BitVector() &&
+        !(Subtarget->hasAVX() && SrcVT.is256BitVector()))
+      return false;
+
+    unsigned Reg = getRegForValue(I->getOperand(0));
+    if (Reg == 0)
+      return false;
+      
+    // No instruction is needed for conversion. Reuse the register used by
+    // the fist operand.
+    updateValueMap(I, Reg);
+    return true;
+  }
   }
 
   return false;
 }
 
 unsigned X86FastISel::X86MaterializeInt(const ConstantInt *CI, MVT VT) {
   if (VT > MVT::i64)
     return 0;

llvm/trunk/test/CodeGen/X86/fast-isel-bitcasts-avx.ll

+; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=+avx -fast-isel -fast-isel-abort=1 -asm-verbose=0 | FileCheck %s
+;
+; Bitcasts between 256-bit vector types are no-ops since no instruction is
+; needed for the conversion.
+
+define <4 x i64> @v8i32_to_v4i64(<8 x i32> %a) {
+;CHECK-LABEL: v8i32_to_v4i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i32> %a to <4 x i64>
+  ret <4 x i64> %1
+}
+
+define <4 x i64> @v16i16_to_v4i64(<16 x i16> %a) {
+;CHECK-LABEL: v16i16_to_v4i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i16> %a to <4 x i64>
+  ret <4 x i64> %1
+}
+
+define <4 x i64> @v32i8_to_v4i64(<32 x i8> %a) {
+;CHECK-LABEL: v32i8_to_v4i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <32 x i8> %a to <4 x i64>
+  ret <4 x i64> %1
+}
+
+define <4 x i64> @v4f64_to_v4i64(<4 x double> %a) {
+;CHECK-LABEL: v4f64_to_v4i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x double> %a to <4 x i64>
+  ret <4 x i64> %1
+}
+
+define <4 x i64> @v8f32_to_v4i64(<8 x float> %a) {
+;CHECK-LABEL: v8f32_to_v4i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x float> %a to <4 x i64>
+  ret <4 x i64> %1
+}
+
+define <8 x i32> @v4i64_to_v8i32(<4 x i64> %a) {
+;CHECK-LABEL: v4i64_to_v8i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i64> %a to <8 x i32>
+  ret <8 x i32> %1
+}
+
+define <8 x i32> @v16i16_to_v8i32(<16 x i16> %a) {
+;CHECK-LABEL: v16i16_to_v8i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i16> %a to <8 x i32>
+  ret <8 x i32> %1
+}
+
+define <8 x i32> @v32i8_to_v8i32(<32 x i8> %a) {
+;CHECK-LABEL: v32i8_to_v8i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <32 x i8> %a to <8 x i32>
+  ret <8 x i32> %1
+}
+
+define <8 x i32> @v4f64_to_v8i32(<4 x double> %a) {
+;CHECK-LABEL: v4f64_to_v8i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x double> %a to <8 x i32>
+  ret <8 x i32> %1
+}
+
+define <8 x i32> @v8f32_to_v8i32(<8 x float> %a) {
+;CHECK-LABEL: v8f32_to_v8i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x float> %a to <8 x i32>
+  ret <8 x i32> %1
+}
+
+define <16 x i16> @v4i64_to_v16i16(<4 x i64> %a) {
+;CHECK-LABEL: v4i64_to_v16i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i64> %a to <16 x i16>
+  ret <16 x i16> %1
+}
+
+define <16 x i16> @v8i32_to_v16i16(<8 x i32> %a) {
+;CHECK-LABEL: v8i32_to_v16i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i32> %a to <16 x i16>
+  ret <16 x i16> %1
+}
+
+define <16 x i16> @v32i8_to_v16i16(<32 x i8> %a) {
+;CHECK-LABEL: v32i8_to_v16i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <32 x i8> %a to <16 x i16>
+  ret <16 x i16> %1
+}
+
+define <16 x i16> @v4f64_to_v16i16(<4 x double> %a) {
+;CHECK-LABEL: v4f64_to_v16i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x double> %a to <16 x i16>
+  ret <16 x i16> %1
+}
+
+define <16 x i16> @v8f32_to_v16i16(<8 x float> %a) {
+;CHECK-LABEL: v8f32_to_v16i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x float> %a to <16 x i16>
+  ret <16 x i16> %1
+}
+
+define <32 x i8> @v16i16_to_v32i8(<16 x i16> %a) {
+;CHECK-LABEL: v16i16_to_v32i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i16> %a to <32 x i8>
+  ret <32 x i8> %1
+}
+
+define <32 x i8> @v4i64_to_v32i8(<4 x i64> %a) {
+;CHECK-LABEL: v4i64_to_v32i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i64> %a to <32 x i8>
+  ret <32 x i8> %1
+}
+
+define <32 x i8> @v8i32_to_v32i8(<8 x i32> %a) {
+;CHECK-LABEL: v8i32_to_v32i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i32> %a to <32 x i8>
+  ret <32 x i8> %1
+}
+
+define <32 x i8> @v4f64_to_v32i8(<4 x double> %a) {
+;CHECK-LABEL: v4f64_to_v32i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x double> %a to <32 x i8>
+  ret <32 x i8> %1
+}
+
+define <32 x i8> @v8f32_to_v32i8(<8 x float> %a) {
+;CHECK-LABEL: v8f32_to_v32i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x float> %a to <32 x i8>
+  ret <32 x i8> %1
+}
+
+define <8 x float> @v32i8_to_v8f32(<32 x i8> %a) {
+;CHECK-LABEL: v32i8_to_v8f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <32 x i8> %a to <8 x float>
+  ret <8 x float> %1
+}
+
+define <8 x float> @v16i16_to_v8f32(<16 x i16> %a) {
+;CHECK-LABEL: v16i16_to_v8f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i16> %a to <8 x float>
+  ret <8 x float> %1
+}
+
+define <8 x float> @v4i64_to_v8f32(<4 x i64> %a) {
+;CHECK-LABEL: v4i64_to_v8f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i64> %a to <8 x float>
+  ret <8 x float> %1
+}
+
+define <8 x float> @v8i32_to_v8f32(<8 x i32> %a) {
+;CHECK-LABEL: v8i32_to_v8f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i32> %a to <8 x float>
+  ret <8 x float> %1
+}
+
+define <8 x float> @v4f64_to_v8f32(<4 x double> %a) {
+;CHECK-LABEL: v4f64_to_v8f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x double> %a to <8 x float>
+  ret <8 x float> %1
+}
+
+define <4 x double> @v8f32_to_v4f64(<8 x float> %a) {
+;CHECK-LABEL: v8f32_to_v4f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x float> %a to <4 x double>
+  ret <4 x double> %1
+}
+
+define <4 x double> @v32i8_to_v4f64(<32 x i8> %a) {
+;CHECK-LABEL: v32i8_to_v4f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <32 x i8> %a to <4 x double>
+  ret <4 x double> %1
+}
+
+define <4 x double> @v16i16_to_v4f64(<16 x i16> %a) {
+;CHECK-LABEL: v16i16_to_v4f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i16> %a to <4 x double>
+  ret <4 x double> %1
+}
+
+define <4 x double> @v4i64_to_v4f64(<4 x i64> %a) {
+;CHECK-LABEL: v4i64_to_v4f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i64> %a to <4 x double>
+  ret <4 x double> %1
+}
+
+define <4 x double> @v8i32_to_v4f64(<8 x i32> %a) {
+;CHECK-LABEL: v8i32_to_v4f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i32> %a to <4 x double>
+  ret <4 x double> %1
+}

llvm/trunk/test/CodeGen/X86/fast-isel-bitcasts.ll

+; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=+sse2 -fast-isel -fast-isel-abort=1 -asm-verbose=0 | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=+avx -fast-isel -fast-isel-abort=1 -asm-verbose=0 | FileCheck %s
+;
+; Bitcasts between 128-bit vector types are no-ops since no instruction is
+; needed for the conversion.
+
+define <2 x i64> @v4i32_to_v2i64(<4 x i32> %a) {
+;CHECK-LABEL: v4i32_to_v2i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i32> %a to <2 x i64>
+  ret <2 x i64> %1
+}
+
+define <2 x i64> @v8i16_to_v2i64(<8 x i16> %a) {
+;CHECK-LABEL: v8i16_to_v2i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i16> %a to <2 x i64>
+  ret <2 x i64> %1
+}
+
+define <2 x i64> @v16i8_to_v2i64(<16 x i8> %a) {
+;CHECK-LABEL: v16i8_to_v2i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i8> %a to <2 x i64>
+  ret <2 x i64> %1
+}
+
+define <2 x i64> @v2f64_to_v2i64(<2 x double> %a) {
+;CHECK-LABEL: v2f64_to_v2i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x double> %a to <2 x i64>
+  ret <2 x i64> %1
+}
+
+define <2 x i64> @v4f32_to_v2i64(<4 x float> %a) {
+;CHECK-LABEL: v4f32_to_v2i64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x float> %a to <2 x i64>
+  ret <2 x i64> %1
+}
+
+define <4 x i32> @v2i64_to_v4i32(<2 x i64> %a) {
+;CHECK-LABEL: v2i64_to_v4i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x i64> %a to <4 x i32>
+  ret <4 x i32> %1
+}
+
+define <4 x i32> @v8i16_to_v4i32(<8 x i16> %a) {
+;CHECK-LABEL: v8i16_to_v4i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i16> %a to <4 x i32>
+  ret <4 x i32> %1
+}
+
+define <4 x i32> @v16i8_to_v4i32(<16 x i8> %a) {
+;CHECK-LABEL: v16i8_to_v4i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i8> %a to <4 x i32>
+  ret <4 x i32> %1
+}
+
+define <4 x i32> @v2f64_to_v4i32(<2 x double> %a) {
+;CHECK-LABEL: v2f64_to_v4i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x double> %a to <4 x i32>
+  ret <4 x i32> %1
+}
+
+define <4 x i32> @v4f32_to_v4i32(<4 x float> %a) {
+;CHECK-LABEL: v4f32_to_v4i32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x float> %a to <4 x i32>
+  ret <4 x i32> %1
+}
+
+define <8 x i16> @v2i64_to_v8i16(<2 x i64> %a) {
+;CHECK-LABEL: v2i64_to_v8i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x i64> %a to <8 x i16>
+  ret <8 x i16> %1
+}
+
+define <8 x i16> @v4i32_to_v8i16(<4 x i32> %a) {
+;CHECK-LABEL: v4i32_to_v8i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i32> %a to <8 x i16>
+  ret <8 x i16> %1
+}
+
+define <8 x i16> @v16i8_to_v8i16(<16 x i8> %a) {
+;CHECK-LABEL: v16i8_to_v8i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i8> %a to <8 x i16>
+  ret <8 x i16> %1
+}
+
+define <8 x i16> @v2f64_to_v8i16(<2 x double> %a) {
+;CHECK-LABEL: v2f64_to_v8i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x double> %a to <8 x i16>
+  ret <8 x i16> %1
+}
+
+define <8 x i16> @v4f32_to_v8i16(<4 x float> %a) {
+;CHECK-LABEL: v4f32_to_v8i16:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x float> %a to <8 x i16>
+  ret <8 x i16> %1
+}
+
+define <16 x i8> @v8i16_to_v16i8(<8 x i16> %a) {
+;CHECK-LABEL: v8i16_to_v16i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i16> %a to <16 x i8>
+  ret <16 x i8> %1
+}
+
+define <16 x i8> @v2i64_to_v16i8(<2 x i64> %a) {
+;CHECK-LABEL: v2i64_to_v16i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x i64> %a to <16 x i8>
+  ret <16 x i8> %1
+}
+
+define <16 x i8> @v4i32_to_v16i8(<4 x i32> %a) {
+;CHECK-LABEL: v4i32_to_v16i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i32> %a to <16 x i8>
+  ret <16 x i8> %1
+}
+
+define <16 x i8> @v2f64_to_v16i8(<2 x double> %a) {
+;CHECK-LABEL: v2f64_to_v16i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x double> %a to <16 x i8>
+  ret <16 x i8> %1
+}
+
+define <16 x i8> @v4f32_to_v16i8(<4 x float> %a) {
+;CHECK-LABEL: v4f32_to_v16i8:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x float> %a to <16 x i8>
+  ret <16 x i8> %1
+}
+
+define <4 x float> @v16i8_to_v4f32(<16 x i8> %a) {
+;CHECK-LABEL: v16i8_to_v4f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i8> %a to <4 x float>
+  ret <4 x float> %1
+}
+
+define <4 x float> @v8i16_to_v4f32(<8 x i16> %a) {
+;CHECK-LABEL: v8i16_to_v4f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i16> %a to <4 x float>
+  ret <4 x float> %1
+}
+
+define <4 x float> @v2i64_to_v4f32(<2 x i64> %a) {
+;CHECK-LABEL: v2i64_to_v4f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x i64> %a to <4 x float>
+  ret <4 x float> %1
+}
+
+define <4 x float> @v4i32_to_v4f32(<4 x i32> %a) {
+;CHECK-LABEL: v4i32_to_v4f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i32> %a to <4 x float>
+  ret <4 x float> %1
+}
+
+define <4 x float> @v2f64_to_v4f32(<2 x double> %a) {
+;CHECK-LABEL: v2f64_to_v4f32:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x double> %a to <4 x float>
+  ret <4 x float> %1
+}
+
+define <2 x double> @v4f32_to_v2f64(<4 x float> %a) {
+;CHECK-LABEL: v4f32_to_v2f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x float> %a to <2 x double>
+  ret <2 x double> %1
+}
+
+define <2 x double> @v16i8_to_v2f64(<16 x i8> %a) {
+;CHECK-LABEL: v16i8_to_v2f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <16 x i8> %a to <2 x double>
+  ret <2 x double> %1
+}
+
+define <2 x double> @v8i16_to_v2f64(<8 x i16> %a) {
+;CHECK-LABEL: v8i16_to_v2f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <8 x i16> %a to <2 x double>
+  ret <2 x double> %1
+}
+
+define <2 x double> @v2i64_to_v2f64(<2 x i64> %a) {
+;CHECK-LABEL: v2i64_to_v2f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <2 x i64> %a to <2 x double>
+  ret <2 x double> %1
+}
+
+define <2 x double> @v4i32_to_v2f64(<4 x i32> %a) {
+;CHECK-LABEL: v4i32_to_v2f64:
+;CHECK-NEXT: .cfi_startproc
+;CHECK-NEXT: ret
+  %1 = bitcast <4 x i32> %a to <2 x double>
+  ret <2 x double> %1
+}