[llvm] r321209 - [X86] Remove zext from vXi32 to vXi64 on indices of gather/scatter instructions if we can prove the pre-extended value is positive.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Wed Dec 20 11:25:33 2017
New Revision: 321209

URL: http://llvm.org/viewvc/llvm-project?rev=321209&view=rev
Log:
[X86] Remove zext from vXi32 to vXi64 on indices of gather/scatter instructions if we can prove the pre-extended value is positive.

Gather/scatter can implicitly sign extend from i32->i64 on indices. So if we know the sign bit of the input to a zext is 0 we can use the implicit extension.

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
    llvm/trunk/test/CodeGen/X86/masked_gather_scatter.ll

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=321209&r1=321208&r2=321209&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Wed Dec 20 11:25:33 2017
@@ -36273,6 +36273,23 @@ static SDValue combineGatherScatter(SDNo
       DCI.AddToWorklist(N);
       return SDValue(N, 0);
     }
+
+    // Try to remove zero extends from 32->64 if we know the sign bit of
+    // the input is zero.
+    if (Index.getOpcode() == ISD::ZERO_EXTEND &&
+        Index.getScalarValueSizeInBits() == 64 &&
+        Index.getOperand(0).getScalarValueSizeInBits() == 32) {
+      if (DAG.SignBitIsZero(Index.getOperand(0))) {
+        SmallVector<SDValue, 5> NewOps(N->op_begin(), N->op_end());
+        NewOps[4] = Index.getOperand(0);
+        DAG.UpdateNodeOperands(N, NewOps);
+        // The original zero extend has less users, add back to worklist in case
+        // it needs to be removed
+        DCI.AddToWorklist(Index.getNode());
+        DCI.AddToWorklist(N);
+        return SDValue(N, 0);
+      }
+    }
   }
 
   // Gather and Scatter instructions use k-registers for masks. The type of

Modified: llvm/trunk/test/CodeGen/X86/masked_gather_scatter.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/masked_gather_scatter.ll?rev=321209&r1=321208&r2=321209&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/masked_gather_scatter.ll (original)
+++ llvm/trunk/test/CodeGen/X86/masked_gather_scatter.ll Wed Dec 20 11:25:33 2017
@@ -2742,3 +2742,48 @@ define void @test_scatter_2i32_index(<2
 }
 declare void @llvm.masked.scatter.v2f64.v2p0f64(<2 x double>, <2 x double*>, i32, <2 x i1>)
 
+define <16 x float> @zext_index(float* %base, <16 x i32> %ind) {
+; KNL_64-LABEL: zext_index:
+; KNL_64:       # %bb.0:
+; KNL_64-NEXT:    vpandd {{.*}}(%rip){1to16}, %zmm0, %zmm1
+; KNL_64-NEXT:    kxnorw %k0, %k0, %k1
+; KNL_64-NEXT:    vgatherdps (%rdi,%zmm1,4), %zmm0 {%k1}
+; KNL_64-NEXT:    retq
+;
+; KNL_32-LABEL: zext_index:
+; KNL_32:       # %bb.0:
+; KNL_32-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; KNL_32-NEXT:    vpandd {{\.LCPI.*}}{1to16}, %zmm0, %zmm1
+; KNL_32-NEXT:    kxnorw %k0, %k0, %k1
+; KNL_32-NEXT:    vgatherdps (%eax,%zmm1,4), %zmm0 {%k1}
+; KNL_32-NEXT:    retl
+;
+; SKX_SMALL-LABEL: zext_index:
+; SKX_SMALL:       # %bb.0:
+; SKX_SMALL-NEXT:    vandps {{.*}}(%rip){1to16}, %zmm0, %zmm1
+; SKX_SMALL-NEXT:    kxnorw %k0, %k0, %k1
+; SKX_SMALL-NEXT:    vgatherdps (%rdi,%zmm1,4), %zmm0 {%k1}
+; SKX_SMALL-NEXT:    retq
+;
+; SKX_LARGE-LABEL: zext_index:
+; SKX_LARGE:       # %bb.0:
+; SKX_LARGE-NEXT:    movabsq ${{\.LCPI.*}}, %rax
+; SKX_LARGE-NEXT:    vandps (%rax){1to16}, %zmm0, %zmm1
+; SKX_LARGE-NEXT:    kxnorw %k0, %k0, %k1
+; SKX_LARGE-NEXT:    vgatherdps (%rdi,%zmm1,4), %zmm0 {%k1}
+; SKX_LARGE-NEXT:    retq
+;
+; SKX_32-LABEL: zext_index:
+; SKX_32:       # %bb.0:
+; SKX_32-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; SKX_32-NEXT:    vandps {{\.LCPI.*}}{1to16}, %zmm0, %zmm1
+; SKX_32-NEXT:    kxnorw %k0, %k0, %k1
+; SKX_32-NEXT:    vgatherdps (%eax,%zmm1,4), %zmm0 {%k1}
+; SKX_32-NEXT:    retl
+  %ind_masked = and <16 x i32> %ind, <i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15>
+  %sext_ind = zext <16 x i32> %ind_masked to <16 x i64>
+  %gep.random = getelementptr float, float *%base, <16 x i64> %sext_ind
+
+  %res = call <16 x float> @llvm.masked.gather.v16f32.v16p0f32(<16 x float*> %gep.random, i32 4, <16 x i1> <i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true>, <16 x float> undef)
+  ret <16 x float>%res
+}