[X86] Handle multiple use freeze(undef) in LowerAVXCONCAT_VECTORS as zero vectors

[RKSimon]

Summary

Replacement for D144903

If we're concatenating freeze(undef) subvector ops with multiple uses then we can't treat them as a wider freeze(undef), but we can replace them with a zero subvector, which is cheap on AVX

[nikic]

LGTM

llvm/lib/Target/X86/X86ISelLowering.cpp

   unsigned NumFreezeUndef = 0;
   unsigned NumZero = 0;
   unsigned NumNonZero = 0;
   unsigned NonZeros = 0;
   for (unsigned i = 0; i != NumOperands; ++i) {
     SDValue SubVec = Op.getOperand(i);
     if (SubVec.isUndef())
       continue;
-    if (ISD::isFreezeUndef(SubVec.getNode()) && SubVec.hasOneUse())
-      ++NumFreezeUndef;
+    if (ISD::isFreezeUndef(SubVec.getNode())) {
+        // If the freeze(undef) has multiple uses then we must fold to zero.
+        if (SubVec.hasOneUse())
+          ++NumFreezeUndef;
+        else
+          ++NumZero;
+    }
     else if (ISD::isBuildVectorAllZeros(SubVec.getNode()))
       ++NumZero;
     else {
       assert(i < sizeof(NonZeros) * CHAR_BIT); // Ensure the shift is in range.
       NonZeros |= 1 << i;
       ++NumNonZero;
     }
   }

llvm/test/CodeGen/X86/avx512-intrinsics.ll

 }
 
 declare <8 x i64> @llvm.x86.avx512.psrlv.q.512(<8 x i64>, <8 x i64>) nounwind readnone
 
 
 define <8 x double> @test_mm256_castpd128_pd256_freeze(<2 x double> %a0) nounwind {
 ; CHECK-LABEL: test_mm256_castpd128_pd256_freeze:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
-; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm1
-; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
-; CHECK-NEXT:    vinsertf64x4 $1, %ymm1, %zmm0, %zmm0
+; CHECK-NEXT:    vmovaps %xmm0, %xmm0
 ; CHECK-NEXT:    ret{{[l|q]}}
   %a1 = freeze <2 x double> poison
   %res = shufflevector <2 x double> %a0, <2 x double> %a1, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 2, i32 3, i32 2, i32 3>
   ret <8 x double> %res
 }
 
 
 define <8 x double> @test_mm256_castpd256_pd256_freeze(<4 x double> %a0) nounwind {
 ; CHECK-LABEL: test_mm256_castpd256_pd256_freeze:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    # kill: def $ymm0 killed $ymm0 def $zmm0
 ; CHECK-NEXT:    ret{{[l|q]}}
   %a1 = freeze <4 x double> poison
   %res = shufflevector <4 x double> %a0, <4 x double> %a1, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
   ret <8 x double> %res
 }
 
 
 define <16 x float> @test_mm256_castps128_ps512_freeze(<4 x float> %a0) nounwind {
 ; CHECK-LABEL: test_mm256_castps128_ps512_freeze:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
-; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm1
-; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
-; CHECK-NEXT:    vinsertf64x4 $1, %ymm1, %zmm0, %zmm0
+; CHECK-NEXT:    vmovaps %xmm0, %xmm0
 ; CHECK-NEXT:    ret{{[l|q]}}
   %a1 = freeze <4 x float> poison
   %res = shufflevector <4 x float> %a0, <4 x float> %a1, <16x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 4, i32 5, i32 6, i32 7, i32 4, i32 5, i32 6, i32 7>
   ret <16 x float> %res
 }
 
 
 define <16 x float> @test_mm256_castps256_ps512_freeze(<8 x float> %a0) nounwind {
 ; CHECK-LABEL: test_mm256_castps256_ps512_freeze:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    # kill: def $ymm0 killed $ymm0 def $zmm0
 ; CHECK-NEXT:    ret{{[l|q]}}
   %a1 = freeze <8 x float> poison
   %res = shufflevector <8 x float> %a0, <8 x float> %a1, <16x 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>
   ret <16 x float> %res
 }
 
 
 define <8 x i64> @test_mm512_castsi128_si512_freeze(<2 x i64> %a0) nounwind {
 ; CHECK-LABEL: test_mm512_castsi128_si512_freeze:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
-; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm1
-; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
-; CHECK-NEXT:    vinsertf64x4 $1, %ymm1, %zmm0, %zmm0
+; CHECK-NEXT:    vmovaps %xmm0, %xmm0
 ; CHECK-NEXT:    ret{{[l|q]}}
   %a1 = freeze <2 x i64> poison
   %res = shufflevector <2 x i64> %a0, <2 x i64> %a1, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 2, i32 3, i32 2, i32 3>
   ret <8 x i64> %res
 }
 
 
 define <8 x i64> @test_mm512_castsi256_si512_pd256_freeze(<4 x i64> %a0) nounwind {

llvm/test/CodeGen/X86/avx512fp16-intrinsics.ll

; CHECK-NEXT:    retq
   %res = shufflevector <8 x half> %a0, <8 x half> %a1, <16 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>
   ret <16 x half> %res
 }
 
 
 define <32 x half> @test_mm512_castph128_ph512_freeze(<8 x half> %a0) nounwind {
 ; CHECK-LABEL: test_mm512_castph128_ph512_freeze:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
-; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm1
-; CHECK-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
-; CHECK-NEXT:    vinsertf64x4 $1, %ymm1, %zmm0, %zmm0
+; CHECK-NEXT:    vmovaps %xmm0, %xmm0
 ; CHECK-NEXT:    retq
   %a1 = freeze <8 x half> poison
   %res = shufflevector <8 x half> %a0, <8 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 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
   ret <32 x half> %res
 }
 
 
 define <32 x half> @test_mm512_castph256_ph512_freeze(<16 x half> %a0) nounwind {
 ; CHECK-LABEL: test_mm512_castph256_ph512_freeze:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    # kill: def $ymm0 killed $ymm0 def $zmm0
 ; CHECK-NEXT:    retq
   %a1 = freeze <16 x half> poison
   %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
 }