SelectionDAG: Handle out-of-bounds index in extract vector element

[chfast]

Summary

This patch correctly handles undef case of EXTRACT_VECTOR_ELT node where the element index is constant and not less than vector size.

[chfast]

Ping.

[chfast]

Ping.

[hfinkel]

LGTM.

[chfast]

Rebase

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

case ISD::SIGN_EXTEND_INREG: {
     }
     break;
   }
   case ISD::EXTRACT_VECTOR_ELT:
     // EXTRACT_VECTOR_ELT of an UNDEF is an UNDEF.
     if (N1.getOpcode() == ISD::UNDEF)
       return getUNDEF(VT);
 
+    // EXTRACT_VECTOR_ELT of out-of-bounds element is an UNDEF
+    if (N2C && N2C->getZExtValue() >= N1.getValueType().getVectorNumElements())
+      return getUNDEF(VT);
+
     // EXTRACT_VECTOR_ELT of CONCAT_VECTORS is often formed while lowering is
     // expanding copies of large vectors from registers.
     if (N2C &&
         N1.getOpcode() == ISD::CONCAT_VECTORS &&
         N1.getNumOperands() > 0) {
       unsigned Factor =
         N1.getOperand(0).getValueType().getVectorNumElements();
       return getNode(ISD::EXTRACT_VECTOR_ELT, DL, VT,

test/CodeGen/X86/extract-store.ll

 ; RUN: llc < %s -o - -mcpu=generic -march=x86-64 -mattr=+sse4.1 | FileCheck %s -check-prefix=SSE41
 ; RUN: llc < %s -o - -mcpu=generic -march=x86-64 -mattr=+avx | FileCheck %s -check-prefix=AVX
 
-define void @pextrb(i8* nocapture %dst, <16 x i8> %foo) {
+; CHECK-LABEL: extract_i8
+define void @extract_i8(i8* nocapture %dst, <16 x i8> %foo) {
 ; AVX: vpextrb
 ; SSE41: pextrb
 ; AVX-NOT: movb
 ; SSE41-NOT: movb
   %vecext = extractelement <16 x i8> %foo, i32 15
   store i8 %vecext, i8* %dst, align 1
   ret void
 }
 
-define void @pextrw(i16* nocapture %dst, <8 x i16> %foo) {
+; CHECK-LABEL: extract_i16
+define void @extract_i16(i16* nocapture %dst, <8 x i16> %foo) {
 ; AVX: vpextrw
 ; SSE41: pextrw
 ; AVX-NOT: movw
 ; SSE41-NOT: movw
-  %vecext = extractelement <8 x i16> %foo, i32 15
+  %vecext = extractelement <8 x i16> %foo, i32 7
+  store i16 %vecext, i16* %dst, align 1
+  ret void
+}
+
+; CHECK-LABEL: extract_i8_undef
+define void @extract_i8_undef(i8* nocapture %dst, <16 x i8> %foo) {
+; AVX-NOT: vpextrb
+; SSE41-NOT: pextrb
+; AVX-NOT: movb
+; SSE41-NOT: movb
+  %vecext = extractelement <16 x i8> %foo, i32 16 ; undef
+  store i8 %vecext, i8* %dst, align 1
+  ret void
+}
+
+; CHECK-LABEL: extract_i16_undef
+define void @extract_i16_undef(i16* nocapture %dst, <8 x i16> %foo) {
+; AVX-NOT: vpextrw
+; SSE41-NOT: pextrw
+; AVX-NOT: movw
+; SSE41-NOT: movw
+  %vecext = extractelement <8 x i16> %foo, i32 9 ; undef
   store i16 %vecext, i16* %dst, align 1
   ret void
 }

test/CodeGen/X86/extractelement-index.ll

-; RUN: llc < %s | FileCheck %s
+; RUN: llc < %s -march=x86-64             | FileCheck %s -check-prefix=X64
+; RUN: llc < %s -march=x86-64 -mattr=+avx | FileCheck %s -check-prefix=AVX
 
-; CHECK-LABEL: extractelement_index_i256_1:
-define i8 @extractelement_index_i256_1(<32 x i8> %a) nounwind {
+
+; CHECK-LABEL: extractelement_index_1:
+define i8 @extractelement_index_1(<32 x i8> %a) nounwind {
+  ; X64:       movaps
+  ; AVX:       vpextrb $1
   %b = extractelement <32 x i8> %a, i256 1
   ret i8 %b
 }
 
-; CHECK-LABEL: extractelement_index_i256_2:
-define i8 @extractelement_index_i256_2(<32 x i8> %a) nounwind {
-  %b = extractelement <32 x i8> %a, i256 60
-  ret i8 %b
+; CHECK-LABEL: extractelement_index_2:
+define i32 @extractelement_index_2(<8 x i32> %a) nounwind {
+  ; X64:       pshufd
+  ; AVX:       vextractf128 $1
+  ; AVX-NEXT:  vpextrd      $3
+  %b = extractelement <8 x i32> %a, i64 7
+  ret i32 %b
+}
+
+; CHECK-LABEL: extractelement_index_3:
+define i32 @extractelement_index_3(<8 x i32> %a) nounwind {
+  ; CHECK-NOT: pextr
+  %b = extractelement <8 x i32> %a, i64 15
+  ret i32 %b
 }
 
-; CHECK-LABEL: extractelement_index_i256_3:
-define i8 @extractelement_index_i256_3(<32 x i8> %a, i256 %i) nounwind {
+; CHECK-LABEL: extractelement_index_4:
+define i32 @extractelement_index_4(<8 x i32> %a) nounwind {
+  ; X64:       movd
+  ; AVX:       vextractf128 $1
+  ; AVX-NEXT:  vmovd
+  %b = extractelement <8 x i32> %a, i256 4
+  ret i32 %b
+}
+
+; CHECK-LABEL: extractelement_index_5:
+define i8 @extractelement_index_5(<32 x i8> %a, i256 %i) nounwind {
+  ; X64:       movaps
+  ; AVX:       vmovaps
   %b = extractelement <32 x i8> %a, i256 %i
   ret i8 %b
 }
 
+; CHECK-LABEL: extractelement_index_6:
+define i8 @extractelement_index_6(<32 x i8> %a) nounwind {
+  ; CHECK-NOT: pextr
+  %b = extractelement <32 x i8> %a, i256 -1
+  ret i8 %b
+}
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