[llvm] r280837 - Don't reduce the width of vector mul if the target doesn't support SSE2.

[Quentin Colombet via llvm-commits]

Hi Wei,

> On Sep 7, 2016, at 11:22 AM, Wei Mi via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: wmi
> Date: Wed Sep  7 13:22:17 2016
> New Revision: 280837
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=280837&view=rev
> Log:
> Don't reduce the width of vector mul if the target doesn't support SSE2.
> 
> The patch is to fix PR30298, which is caused by rL272694. The solution is to
> bail out if the target has no SSE2.
> 
> Differential Revision: https://reviews.llvm.org/D24288
> 
> Added:
>    llvm/trunk/test/CodeGen/X86/pr30298.ll
> Modified:
>    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
> 
> Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=280837&r1=280836&r2=280837&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
> +++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Wed Sep  7 13:22:17 2016
> @@ -28077,7 +28077,8 @@ static SDValue reduceVMULWidth(SDNode *N
>                                const X86Subtarget &Subtarget) {
>   // pmulld is supported since SSE41. It is better to use pmulld
>   // instead of pmullw+pmulhw.
> -  if (Subtarget.hasSSE41())
> +  // pmullw/pmulhw are not supported by SSE.
> +  if (Subtarget.hasSSE41() || !Subtarget.hasSSE2())
>     return SDValue();
> 
>   ShrinkMode Mode;
> 
> Added: llvm/trunk/test/CodeGen/X86/pr30298.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/pr30298.ll?rev=280837&view=auto
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/pr30298.ll (added)
> +++ llvm/trunk/test/CodeGen/X86/pr30298.ll Wed Sep  7 13:22:17 2016

Please use meaningful name for the filename.

> @@ -0,0 +1,43 @@
> +; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
> +; RUN: llc -mtriple=i386-pc-linux-gnu -mattr=+sse < %s | FileCheck %s

Add a comment on what this test case is checking. Putting the PR number here would be a good idea.

Cheers,
-Quentin
> +
> + at c = external global i32*, align 8
> +
> +define void @mul_2xi8(i8* nocapture readonly %a, i8* nocapture readonly %b, i64 %index) nounwind {
> +; CHECK-LABEL: mul_2xi8:
> +; CHECK:       # BB#0: # %entry
> +; CHECK-NEXT:    pushl %ebx
> +; CHECK-NEXT:    pushl %edi
> +; CHECK-NEXT:    pushl %esi
> +; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %eax
> +; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %ecx
> +; CHECK-NEXT:    movl {{[0-9]+}}(%esp), %edx
> +; CHECK-NEXT:    movl c, %esi
> +; CHECK-NEXT:    movzbl 1(%edx,%ecx), %edi
> +; CHECK-NEXT:    movzbl (%edx,%ecx), %edx
> +; CHECK-NEXT:    movzbl 1(%eax,%ecx), %ebx
> +; CHECK-NEXT:    movzbl (%eax,%ecx), %eax
> +; CHECK-NEXT:    imull %edx, %eax
> +; CHECK-NEXT:    imull %edi, %ebx
> +; CHECK-NEXT:    movl %ebx, 4(%esi,%ecx,4)
> +; CHECK-NEXT:    movl %eax, (%esi,%ecx,4)
> +; CHECK-NEXT:    popl %esi
> +; CHECK-NEXT:    popl %edi
> +; CHECK-NEXT:    popl %ebx
> +; CHECK-NEXT:    retl
> +entry:
> +  %pre = load i32*, i32** @c
> +  %tmp6 = getelementptr inbounds i8, i8* %a, i64 %index
> +  %tmp7 = bitcast i8* %tmp6 to <2 x i8>*
> +  %wide.load = load <2 x i8>, <2 x i8>* %tmp7, align 1
> +  %tmp8 = zext <2 x i8> %wide.load to <2 x i32>
> +  %tmp10 = getelementptr inbounds i8, i8* %b, i64 %index
> +  %tmp11 = bitcast i8* %tmp10 to <2 x i8>*
> +  %wide.load17 = load <2 x i8>, <2 x i8>* %tmp11, align 1
> +  %tmp12 = zext <2 x i8> %wide.load17 to <2 x i32>
> +  %tmp13 = mul nuw nsw <2 x i32> %tmp12, %tmp8
> +  %tmp14 = getelementptr inbounds i32, i32* %pre, i64 %index
> +  %tmp15 = bitcast i32* %tmp14 to <2 x i32>*
> +  store <2 x i32> %tmp13, <2 x i32>* %tmp15, align 4
> +  ret void
> +}
> 
> 
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