[DirectX backend] change MinVectorRegisterBitWidth to 32.

[python3kgae]

Summary

This is to avoid vector-combine generate vector4 on float.

[python3kgae]

Simplify test.

[python3kgae]

Remove check-not which is not needed.

[beanz]

LGTM

llvm/lib/Target/DirectX/DirectXTargetTransformInfo.h

class DirectXTTIImpl : public BasicTTIImplBase<DirectXTTIImpl> {
 
   const DirectXSubtarget *getST() const { return ST; }
   const DirectXTargetLowering *getTLI() const { return TLI; }
 
 public:
   explicit DirectXTTIImpl(const DirectXTargetMachine *TM, const Function &F)
       : BaseT(TM, F.getParent()->getDataLayout()), ST(TM->getSubtargetImpl(F)),
         TLI(ST->getTargetLowering()) {}
+  unsigned getMinVectorRegisterBitWidth() const { return 32; }
 };
 } // namespace llvm
 
 #endif // LLVM_DIRECTX_DIRECTXTARGETTRANSFORMINFO_H

llvm/test/CodeGen/DirectX/min_vec_size.ll

+; RUN: opt -S -vector-combine < %s | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i1:32-i8:8-i16:16-i32:32-i64:64-f16:16-f32:32-f64:64-n8:16:32:64"
+target triple = "dxil-unknown-shadermodel6.7-library"
+
[e-mail]. = external local_unnamed_addr constant { float, <2 x float> }
+
+; Make sure vec combine min vec size is 1 instead of 4 for float.
+; CHECK:load <1 x float>
+; CHECK-NOT:<4 x float>
+
+; Function Attrs: mustprogress nofree norecurse nosync nounwind readnone willreturn
+define noundef <2 x float> @"?foo@@YAT?$__vector@M$01@__clang@@XZ"() local_unnamed_addr #0 {
+entry:
+  %0 = load float, ptr @A.cb., align 8, !tbaa !3
+  %splat.splatinsert = insertelement <2 x float> poison, float %0, i64 0
+  %splat.splat = shufflevector <2 x float> %splat.splatinsert, <2 x float> poison, <2 x i32> zeroinitializer
+  %1 = load <2 x float>, ptr getelementptr inbounds ({ float, <2 x float> }, ptr @A.cb., i32 0, i32 1), align 8, !tbaa !7
+  %add = fadd <2 x float> %1, %splat.splat
+  ret <2 x float> %add
+}
+
+attributes #0 = { mustprogress nofree norecurse nosync nounwind readnone willreturn "frame-pointer"="none" "min-legal-vector-width"="64" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+
+!llvm.module.flags = !{!0}
+!hlsl.cbufs = !{!1}
+!llvm.ident = !{!2}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{ptr @A.cb., !"A.cb.ty", i32 0, i32 -1, i32 0}
+!2 = !{!"clang version 16.0.0 (https://github.com/llvm/llvm-project.git 5e0f6f41b63b362da14f0b71acc38779202dfe9c)"}
+!3 = !{!4, !4, i64 0}
+!4 = !{!"float", !5, i64 0}
+!5 = !{!"omnipotent char", !6, i64 0}
+!6 = !{!"Simple C++ TBAA"}
+!7 = !{!5, !5, i64 0}