[llvm] [X86] getScalarMaskingNode - if the mask is zero just return the preserved source value (PR #153575)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

<details>
<summary>Changes</summary>

We already do the reverse if the mask is one, so I added the other case.

This just handles the fold upon creation of the X86ISD::SELECTS node - an alternative would be to add a full combineSELECTS combine to handle cases where this appears in later folds?

I had to adjust the test case for #<!-- -->98306 as AFAICT it'd been over reduced

Fixes #<!-- -->153570

---
Full diff: https://github.com/llvm/llvm-project/pull/153575.diff


3 Files Affected:

- (modified) llvm/lib/Target/X86/X86ISelLowering.cpp (+1-3) 
- (modified) llvm/test/CodeGen/X86/avx512cfmulsh-instrinsics.ll (+3-3) 
- (modified) llvm/test/CodeGen/X86/avx512fp16-intrinsics.ll (+15) 


``````````diff
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 97cdf5b784bc0..00623fa8c8972 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -26261,10 +26261,8 @@ static SDValue getScalarMaskingNode(SDValue Op, SDValue Mask,
                                     SDValue PreservedSrc,
                                     const X86Subtarget &Subtarget,
                                     SelectionDAG &DAG) {
-
   if (auto *MaskConst = dyn_cast<ConstantSDNode>(Mask))
-    if (MaskConst->getZExtValue() & 0x1)
-      return Op;
+    return (MaskConst->getZExtValue() & 0x1) ? Op : PreservedSrc;
 
   MVT VT = Op.getSimpleValueType();
   SDLoc dl(Op);
diff --git a/llvm/test/CodeGen/X86/avx512cfmulsh-instrinsics.ll b/llvm/test/CodeGen/X86/avx512cfmulsh-instrinsics.ll
index e449c7192e4bf..b60d7a5463d6b 100644
--- a/llvm/test/CodeGen/X86/avx512cfmulsh-instrinsics.ll
+++ b/llvm/test/CodeGen/X86/avx512cfmulsh-instrinsics.ll
@@ -278,14 +278,14 @@ define <4 x float> @test_int_x86_avx512fp16_maskz_cfcmadd_sh(<4 x float> %x0, <4
   ret <4 x float> %res
 }
 
-define <4 x float> @PR98306() {
+define <4 x float> @PR98306(i8 %m) {
 ; CHECK-LABEL: PR98306:
 ; CHECK:       ## %bb.0:
-; CHECK-NEXT:    kxorw %k0, %k0, %k1
+; CHECK-NEXT:    kmovd %edi, %k1
 ; CHECK-NEXT:    vmovaps {{.*#+}} xmm1 = [7.8125E-3,1.050912E+6,4.203776E+6,1.6815616E+7]
 ; CHECK-NEXT:    vmovaps {{.*#+}} xmm0 = [3.2E+1,4.03288064E+8,8.0658432E+8,1.61318502E+9]
 ; CHECK-NEXT:    vfmaddcsh {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm1, %xmm0 {%k1} {z}
 ; CHECK-NEXT:    retq
-  %res = call <4 x float> @llvm.x86.avx512fp16.maskz.vfmadd.csh(<4 x float> <float 7.812500e-03, float 0x4130092000000000, float 0x4150094000000000, float 0x4170096000000000>, <4 x float> <float 2.000000e+00, float 0x4188098000000000, float 0x4198099000000000, float 0x41A809A000000000>, <4 x float> <float 3.200000e+01, float 0x41B809B000000000, float 0x41C809C000000000, float 0x41D809D000000000>, i8 0, i32 4)
+  %res = call <4 x float> @llvm.x86.avx512fp16.maskz.vfmadd.csh(<4 x float> <float 7.812500e-03, float 0x4130092000000000, float 0x4150094000000000, float 0x4170096000000000>, <4 x float> <float 2.000000e+00, float 0x4188098000000000, float 0x4198099000000000, float 0x41A809A000000000>, <4 x float> <float 3.200000e+01, float 0x41B809B000000000, float 0x41C809C000000000, float 0x41D809D000000000>, i8 %m, i32 4)
   ret <4 x float> %res
 }
diff --git a/llvm/test/CodeGen/X86/avx512fp16-intrinsics.ll b/llvm/test/CodeGen/X86/avx512fp16-intrinsics.ll
index 627a94799424c..89410a9c1b476 100644
--- a/llvm/test/CodeGen/X86/avx512fp16-intrinsics.ll
+++ b/llvm/test/CodeGen/X86/avx512fp16-intrinsics.ll
@@ -1361,3 +1361,18 @@ define <32 x half> @test_mm512_castph256_ph512_freeze(<16 x half> %a0) nounwind
   %res = shufflevector <16 x half> %a0, <16 x half> %a1, <32 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 16, i32 17, i32 18, i32 19, i32 20, i32 21, i32 22, i32 23, i32 24, i32 25, i32 26, i32 27, i32 28, i32 29, i32 30, i32 31>
   ret <32 x half> %res
 }
+
+define <8 x half> @PR153570(ptr %p) {
+; CHECK-LABEL: PR153570:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vmovsh {{.*#+}} xmm0 = [2.0E+0,0.0E+0,0.0E+0,0.0E+0,0.0E+0,0.0E+0,0.0E+0,0.0E+0]
+; CHECK-NEXT:    vmovsh {{.*#+}} xmm1 = [1.0E+0,0.0E+0,0.0E+0,0.0E+0,0.0E+0,0.0E+0,0.0E+0,0.0E+0]
+; CHECK-NEXT:    vmulsh {rn-sae}, %xmm0, %xmm1, %xmm0
+; CHECK-NEXT:    vxorps %xmm1, %xmm1, %xmm1
+; CHECK-NEXT:    vmovaps %xmm1, (%rdi)
+; CHECK-NEXT:    retq
+  %r = tail call <8 x half> @llvm.x86.avx512fp16.mask.mul.sh.round(<8 x half> <half 0xH3C00, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000>, <8 x half> <half 0xH4000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000>, <8 x half> zeroinitializer, i8 0, i32 8)
+  store <8 x half> %r, ptr %p, align 16
+  %r1 = tail call <8 x half> @llvm.x86.avx512fp16.mask.mul.sh.round(<8 x half> <half 0xH3C00, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000>, <8 x half> <half 0xH4000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000, half 0xH0000>, <8 x half> zeroinitializer, i8 1, i32 8)
+  ret <8 x half> %r1
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/153575