[X86] combineConcatVectorOps - add concatenation handling for consecutive extracts of upper subvectors

[RKSimon]

We already fold concat(extract_subvector(x,0), extract_subvector(x,numsubelts)) -> (wider lower half) extract_subvector(x,0)

This patch extends this handling for the concat(extract_subvector(x,c), extract_subvector(x,c+numsubelts)) -> (wider upper half) extract_subvector(x,c) case as well

[llvmbot]

@llvm/pr-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

Changes

We already fold concat(extract_subvector(x,0), extract_subvector(x,numsubelts)) -> (wider lower half) extract_subvector(x,0)

This patch extends this handling for the concat(extract_subvector(x,c), extract_subvector(x,c+numsubelts)) -> (wider upper half) extract_subvector(x,c) case as well

---

Full diff: https://github.com/llvm/llvm-project/pull/132389.diff

3 Files Affected:

• (modified) llvm/lib/Target/X86/X86ISelLowering.cpp (+11-5)
• (modified) llvm/test/CodeGen/X86/matrix-multiply.ll (-4)
• (modified) llvm/test/CodeGen/X86/vector-shuffle-combining-avx512f.ll (+2-5)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index f6b5d4af5ba4e..4f4254ce6fb0e 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -57955,13 +57955,19 @@ static SDValue combineConcatVectorOps(const SDLoc &DL, MVT VT,
                            DAG.getBitcast(VT, Src1.getOperand(0)),
                            DAG.getTargetConstant(0x31, DL, MVT::i8));
       }
-      // concat(extract_subvector(x,lo), extract_subvector(x,hi)) -> x.
+      // Widen extract_subvector
+      // concat(extract_subvector(x,lo), extract_subvector(x,hi))
+      // --> extract_subvector(x,lo)
+      unsigned NumSubElts0 = Src0.getValueType().getVectorNumElements();
       if (Src0.getOperand(0) == Src1.getOperand(0) &&
-          Src0.getConstantOperandAPInt(1) == 0 &&
+          (Src0.getConstantOperandAPInt(1) == 0 ||
+           Src0.getConstantOperandAPInt(1) == (NumSrcElts0 / 2)) &&
           Src1.getConstantOperandAPInt(1) ==
-              Src0.getValueType().getVectorNumElements()) {
-        return DAG.getBitcast(VT, extractSubVector(Src0.getOperand(0), 0, DAG,
-                                                   DL, VT.getSizeInBits()));
+              (Src0.getConstantOperandAPInt(1) + NumSubElts0)) {
+        return DAG.getBitcast(VT,
+                              extractSubVector(Src0.getOperand(0),
+                                               Src0.getConstantOperandVal(1),
+                                               DAG, DL, VT.getSizeInBits()));
       }
     }
   }
diff --git a/llvm/test/CodeGen/X86/matrix-multiply.ll b/llvm/test/CodeGen/X86/matrix-multiply.ll
index 9763893d3daa2..9b8816bd11f70 100644
--- a/llvm/test/CodeGen/X86/matrix-multiply.ll
+++ b/llvm/test/CodeGen/X86/matrix-multiply.ll
@@ -1036,10 +1036,6 @@ define <16 x float> @test_mul4x4_f32(<16 x float> %a0, <16 x float> %a1) nounwin
 ;
 ; AVX512-LABEL: test_mul4x4_f32:
 ; AVX512:       # %bb.0: # %entry
-; AVX512-NEXT:    vextractf32x4 $2, %zmm1, %xmm2
-; AVX512-NEXT:    vextractf32x4 $3, %zmm1, %xmm3
-; AVX512-NEXT:    vinsertf128 $1, %xmm3, %ymm2, %ymm2
-; AVX512-NEXT:    vinsertf64x4 $1, %ymm2, %zmm1, %zmm1
 ; AVX512-NEXT:    vshufps {{.*#+}} zmm2 = zmm1[1,1,1,1,5,5,5,5,9,9,9,9,13,13,13,13]
 ; AVX512-NEXT:    vshuff64x2 {{.*#+}} zmm3 = zmm0[2,3,2,3,2,3,2,3]
 ; AVX512-NEXT:    vmulps %zmm2, %zmm3, %zmm2
diff --git a/llvm/test/CodeGen/X86/vector-shuffle-combining-avx512f.ll b/llvm/test/CodeGen/X86/vector-shuffle-combining-avx512f.ll
index a28eba39685cb..400a3e835307f 100644
--- a/llvm/test/CodeGen/X86/vector-shuffle-combining-avx512f.ll
+++ b/llvm/test/CodeGen/X86/vector-shuffle-combining-avx512f.ll
@@ -997,15 +997,12 @@ define <8 x double> @concat_vpermilvar_v8f64_v2f64(<2 x double> %a0, <2 x double
 ;
 ; X64-LABEL: concat_vpermilvar_v8f64_v2f64:
 ; X64:       # %bb.0:
+; X64-NEXT:    # kill: def $xmm2 killed $xmm2 def $ymm2
 ; X64-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
-; X64-NEXT:    vextractf32x4 $2, %zmm4, %xmm5
-; X64-NEXT:    vextractf32x4 $3, %zmm4, %xmm6
-; X64-NEXT:    vpermilpd %xmm5, %xmm2, %xmm2
-; X64-NEXT:    vpermilpd %xmm6, %xmm3, %xmm3
 ; X64-NEXT:    vinsertf128 $1, %xmm3, %ymm2, %ymm2
 ; X64-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
-; X64-NEXT:    vpermilpd %ymm4, %ymm0, %ymm0
 ; X64-NEXT:    vinsertf64x4 $1, %ymm2, %zmm0, %zmm0
+; X64-NEXT:    vpermilpd %zmm4, %zmm0, %zmm0
 ; X64-NEXT:    retq
   %m0 = shufflevector <8 x i64> %m, <8 x i64> poison, <2 x i32> <i32 0, i32 1>
   %m1 = shufflevector <8 x i64> %m, <8 x i64> poison, <2 x i32> <i32 2, i32 3>