[PATCH] D21660: [X86][AVX] Peek through bitcasts to find the source of broadcasts

[Simon Pilgrim via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: mkuper, ab, spatel, andreadb.
RKSimon added a subscriber: llvm-commits.
RKSimon set the repository for this revision to rL LLVM.

AVX1 can only broadcast vectors as floats/doubles, so for 256-bit vectors we insert bitcasts if we are shuffling v8i32/v4i64 types. Unfortunately the presence of these bitcasts prevents the current broadcast lowering code from peeking through cases where we have concatenated / extracted vectors to create the 256-bit vectors.

This patch allows us to peek through bitcasts as long as the number of elements doesn't change (i.e. element bitwidth is the same) so the broadcast index is not affected.

Note this bitcast peek is different from the stage later on which doesn't care about the type and is just trying to find a load node.

Repository:
  rL LLVM

http://reviews.llvm.org/D21660

Files:
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/avx-vbroadcast.ll
  test/CodeGen/X86/vector-shuffle-256-v4.ll

Index: test/CodeGen/X86/vector-shuffle-256-v4.ll
===================================================================
--- test/CodeGen/X86/vector-shuffle-256-v4.ll
+++ test/CodeGen/X86/vector-shuffle-256-v4.ll
@@ -1320,8 +1320,7 @@
 define <4 x i64> @splat_mem_v4i64_from_v2i64(<2 x i64>* %ptr) {
 ; AVX1-LABEL: splat_mem_v4i64_from_v2i64:
 ; AVX1:       # BB#0:
-; AVX1-NEXT:    vmovddup {{.*#+}} xmm0 = mem[0,0]
-; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; AVX1-NEXT:    vbroadcastsd (%rdi), %ymm0
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: splat_mem_v4i64_from_v2i64:
Index: test/CodeGen/X86/avx-vbroadcast.ll
===================================================================
--- test/CodeGen/X86/avx-vbroadcast.ll
+++ test/CodeGen/X86/avx-vbroadcast.ll
@@ -173,14 +173,12 @@
 ; X32-LABEL: load_splat_8i32_4i32_33333333:
 ; X32:       ## BB#0: ## %entry
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-NEXT:    vpermilps {{.*#+}} xmm0 = mem[3,3,3,3]
-; X32-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; X32-NEXT:    vbroadcastss 12(%eax), %ymm0
 ; X32-NEXT:    retl
 ;
 ; X64-LABEL: load_splat_8i32_4i32_33333333:
 ; X64:       ## BB#0: ## %entry
-; X64-NEXT:    vpermilps {{.*#+}} xmm0 = mem[3,3,3,3]
-; X64-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; X64-NEXT:    vbroadcastss 12(%rdi), %ymm0
 ; X64-NEXT:    retq
 entry:
   %ld = load <4 x i32>, <4 x i32>* %ptr
@@ -277,16 +275,12 @@
 ; X32-LABEL: load_splat_4i64_2i64_1111:
 ; X32:       ## BB#0: ## %entry
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-NEXT:    vmovaps (%eax), %xmm0
-; X32-NEXT:    vmovhlps {{.*#+}} xmm0 = xmm0[1,1]
-; X32-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; X32-NEXT:    vbroadcastsd 8(%eax), %ymm0
 ; X32-NEXT:    retl
 ;
 ; X64-LABEL: load_splat_4i64_2i64_1111:
 ; X64:       ## BB#0: ## %entry
-; X64-NEXT:    vmovaps (%rdi), %xmm0
-; X64-NEXT:    vmovhlps {{.*#+}} xmm0 = xmm0[1,1]
-; X64-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; X64-NEXT:    vbroadcastsd 8(%rdi), %ymm0
 ; X64-NEXT:    retq
 entry:
   %ld = load <2 x i64>, <2 x i64>* %ptr
Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -8526,6 +8526,13 @@
   SDValue V = V1;
   for (;;) {
     switch (V.getOpcode()) {
+    case ISD::BITCAST: {
+      SDValue VSrc = V.getOperand(0);
+      if (NumElts != VSrc.getSimpleValueType().getVectorNumElements())
+        break;
+      V = V.getOperand(0);
+      continue;
+    }
     case ISD::CONCAT_VECTORS: {
       int OperandSize = Mask.size() / V.getNumOperands();
       V = V.getOperand(BroadcastIdx / OperandSize);


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