[X86] Fold MOVMSK(ICMP_SGT(X,-1)) -> NOT(MOVMSK(X)))

Noticed while triaging PR37506
llvm · Dec 6, 2020 · 0101fb7 · 0101fb7
1 parent d6941a1
commit 0101fb7
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Showing 2 changed files with 17 additions and 12 deletions.
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -47378,7 +47378,7 @@ static SDValue combineMOVMSK(SDNode *N, SelectionDAG &DAG,
       Src.getOperand(0).getScalarValueSizeInBits() == EltWidth)
     return DAG.getNode(X86ISD::MOVMSK, SDLoc(N), VT, Src.getOperand(0));
 
-  // Fold movmsk(not(x)) -> not(movmsk) to improve folding of movmsk results
+  // Fold movmsk(not(x)) -> not(movmsk(x)) to improve folding of movmsk results
   // with scalar comparisons.
   if (SDValue NotSrc = IsNOT(Src, DAG)) {
     SDLoc DL(N);
@@ -47389,6 +47389,17 @@ static SDValue combineMOVMSK(SDNode *N, SelectionDAG &DAG,
                        DAG.getConstant(NotMask, DL, VT));
   }
 
+  // Fold movmsk(icmp_sgt(x,-1)) -> not(movmsk(x)) to improve folding of movmsk
+  // results with scalar comparisons.
+  if (Src.getOpcode() == X86ISD::PCMPGT &&
+      ISD::isBuildVectorAllOnes(Src.getOperand(1).getNode())) {
+    SDLoc DL(N);
+    APInt NotMask = APInt::getLowBitsSet(NumBits, NumElts);
+    return DAG.getNode(ISD::XOR, DL, VT,
+                       DAG.getNode(X86ISD::MOVMSK, DL, VT, Src.getOperand(0)),
+                       DAG.getConstant(NotMask, DL, VT));
+  }
+
   // Simplify the inputs.
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   APInt DemandedMask(APInt::getAllOnesValue(NumBits));

diff --git a/llvm/test/CodeGen/X86/combine-movmsk.ll b/llvm/test/CodeGen/X86/combine-movmsk.ll
@@ -178,22 +178,20 @@ define i1 @pmovmskb_allof_bitcast_v4f32(<4 x float> %a0) {
   ret i1 %5
 }
 
-; FIXME: MOVMSK(ICMP_SGT(X,-1)) -> NOT(MOVMSK(X)))
+; MOVMSK(ICMP_SGT(X,-1)) -> NOT(MOVMSK(X)))
 define i1 @movmskps_allof_v4i32_positive(<4 x i32> %a0) {
 ; SSE-LABEL: movmskps_allof_v4i32_positive:
 ; SSE:       # %bb.0:
-; SSE-NEXT:    pcmpeqd %xmm1, %xmm1
-; SSE-NEXT:    pcmpgtd %xmm1, %xmm0
 ; SSE-NEXT:    movmskps %xmm0, %eax
+; SSE-NEXT:    xorl $15, %eax
 ; SSE-NEXT:    cmpl $15, %eax
 ; SSE-NEXT:    sete %al
 ; SSE-NEXT:    retq
 ;
 ; AVX-LABEL: movmskps_allof_v4i32_positive:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    vpcmpeqd %xmm1, %xmm1, %xmm1
-; AVX-NEXT:    vpcmpgtd %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    vmovmskps %xmm0, %eax
+; AVX-NEXT:    xorl $15, %eax
 ; AVX-NEXT:    cmpl $15, %eax
 ; AVX-NEXT:    sete %al
 ; AVX-NEXT:    retq
@@ -208,19 +206,15 @@ define i1 @movmskps_allof_v4i32_positive(<4 x i32> %a0) {
 define i1 @pmovmskb_noneof_v16i8_positive(<16 x i8> %a0) {
 ; SSE-LABEL: pmovmskb_noneof_v16i8_positive:
 ; SSE:       # %bb.0:
-; SSE-NEXT:    pcmpeqd %xmm1, %xmm1
-; SSE-NEXT:    pcmpgtb %xmm1, %xmm0
 ; SSE-NEXT:    pmovmskb %xmm0, %eax
-; SSE-NEXT:    testl %eax, %eax
+; SSE-NEXT:    xorl $65535, %eax # imm = 0xFFFF
 ; SSE-NEXT:    sete %al
 ; SSE-NEXT:    retq
 ;
 ; AVX-LABEL: pmovmskb_noneof_v16i8_positive:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    vpcmpeqd %xmm1, %xmm1, %xmm1
-; AVX-NEXT:    vpcmpgtb %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    vpmovmskb %xmm0, %eax
-; AVX-NEXT:    testl %eax, %eax
+; AVX-NEXT:    xorl $65535, %eax # imm = 0xFFFF
 ; AVX-NEXT:    sete %al
 ; AVX-NEXT:    retq
   %1 = icmp sgt <16 x i8> %a0, <i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1>