[llvm] r337518 - [DAGCombiner] Fold X - (-Y *Z) -> X + (Y * Z)

[Craig Topper via llvm-commits]

Author: ctopper
Date: Thu Jul 19 18:40:03 2018
New Revision: 337518

URL: http://llvm.org/viewvc/llvm-project?rev=337518&view=rev
Log:
[DAGCombiner] Fold X - (-Y *Z) -> X + (Y * Z)

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    llvm/trunk/test/CodeGen/X86/combine-srem.ll

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=337518&r1=337517&r2=337518&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Thu Jul 19 18:40:03 2018
@@ -2629,6 +2629,24 @@ SDValue DAGCombiner::visitSUB(SDNode *N)
     return DAG.getNode(ISD::SUB, DL, VT, N0.getOperand(0),
                        N0.getOperand(1).getOperand(0));
 
+  // fold (X - (-Y * Z)) -> (X + (Y * Z))
+  if (N1.getOpcode() == ISD::MUL && N1.hasOneUse()) {
+    if (N1.getOperand(0).getOpcode() == ISD::SUB &&
+        isNullConstantOrNullSplatConstant(N1.getOperand(0).getOperand(0))) {
+      SDValue Mul = DAG.getNode(ISD::MUL, DL, VT,
+                                N1.getOperand(0).getOperand(1),
+                                N1.getOperand(1));
+      return DAG.getNode(ISD::ADD, DL, VT, N0, Mul);
+    }
+    if (N1.getOperand(1).getOpcode() == ISD::SUB &&
+        isNullConstantOrNullSplatConstant(N1.getOperand(1).getOperand(0))) {
+      SDValue Mul = DAG.getNode(ISD::MUL, DL, VT,
+                                N1.getOperand(0),
+                                N1.getOperand(1).getOperand(1));
+      return DAG.getNode(ISD::ADD, DL, VT, N0, Mul);
+    }
+  }
+
   // If either operand of a sub is undef, the result is undef
   if (N0.isUndef())
     return N0;

Modified: llvm/trunk/test/CodeGen/X86/combine-srem.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/combine-srem.ll?rev=337518&r1=337517&r2=337518&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/combine-srem.ll (original)
+++ llvm/trunk/test/CodeGen/X86/combine-srem.ll Thu Jul 19 18:40:03 2018
@@ -55,13 +55,13 @@ define <4 x i32> @combine_vec_srem_by_ne
 define i32 @combine_srem_by_minsigned(i32 %x) {
 ; CHECK-LABEL: combine_srem_by_minsigned:
 ; CHECK:       # %bb.0:
+; CHECK-NEXT:    # kill: def $edi killed $edi def $rdi
 ; CHECK-NEXT:    movl %edi, %eax
 ; CHECK-NEXT:    sarl $31, %eax
 ; CHECK-NEXT:    shrl %eax
 ; CHECK-NEXT:    addl %edi, %eax
 ; CHECK-NEXT:    andl $-2147483648, %eax # imm = 0x80000000
-; CHECK-NEXT:    subl %eax, %edi
-; CHECK-NEXT:    movl %edi, %eax
+; CHECK-NEXT:    leal (%rax,%rdi), %eax
 ; CHECK-NEXT:    retq
   %1 = srem i32 %x, -2147483648
   ret i32 %1
@@ -359,10 +359,9 @@ define <4 x i32> @combine_vec_srem_by_po
 ; SSE-NEXT:    psrad $1, %xmm1
 ; SSE-NEXT:    pblendw {{.*#+}} xmm1 = xmm1[0,1,2,3],xmm2[4,5,6,7]
 ; SSE-NEXT:    pblendw {{.*#+}} xmm1 = xmm1[0,1],xmm3[2,3],xmm1[4,5],xmm3[6,7]
-; SSE-NEXT:    pxor %xmm2, %xmm2
-; SSE-NEXT:    psubd %xmm1, %xmm2
-; SSE-NEXT:    pmulld {{.*}}(%rip), %xmm2
-; SSE-NEXT:    psubd %xmm2, %xmm0
+; SSE-NEXT:    pmulld {{.*}}(%rip), %xmm1
+; SSE-NEXT:    paddd %xmm0, %xmm1
+; SSE-NEXT:    movdqa %xmm1, %xmm0
 ; SSE-NEXT:    retq
 ;
 ; AVX1-LABEL: combine_vec_srem_by_pow2b_neg:
@@ -383,10 +382,8 @@ define <4 x i32> @combine_vec_srem_by_po
 ; AVX1-NEXT:    vpsrad $1, %xmm1, %xmm1
 ; AVX1-NEXT:    vpblendw {{.*#+}} xmm1 = xmm1[0,1,2,3],xmm3[4,5,6,7]
 ; AVX1-NEXT:    vpblendw {{.*#+}} xmm1 = xmm1[0,1],xmm2[2,3],xmm1[4,5],xmm2[6,7]
-; AVX1-NEXT:    vpxor %xmm2, %xmm2, %xmm2
-; AVX1-NEXT:    vpsubd %xmm1, %xmm2, %xmm1
 ; AVX1-NEXT:    vpmulld {{.*}}(%rip), %xmm1, %xmm1
-; AVX1-NEXT:    vpsubd %xmm1, %xmm0, %xmm0
+; AVX1-NEXT:    vpaddd %xmm1, %xmm0, %xmm0
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: combine_vec_srem_by_pow2b_neg:
@@ -395,10 +392,8 @@ define <4 x i32> @combine_vec_srem_by_po
 ; AVX2-NEXT:    vpsrlvd {{.*}}(%rip), %xmm1, %xmm1
 ; AVX2-NEXT:    vpaddd %xmm1, %xmm0, %xmm1
 ; AVX2-NEXT:    vpsravd {{.*}}(%rip), %xmm1, %xmm1
-; AVX2-NEXT:    vpxor %xmm2, %xmm2, %xmm2
-; AVX2-NEXT:    vpsubd %xmm1, %xmm2, %xmm1
 ; AVX2-NEXT:    vpmulld {{.*}}(%rip), %xmm1, %xmm1
-; AVX2-NEXT:    vpsubd %xmm1, %xmm0, %xmm0
+; AVX2-NEXT:    vpaddd %xmm1, %xmm0, %xmm0
 ; AVX2-NEXT:    retq
   %1 = srem <4 x i32> %x, <i32 -2, i32 -4, i32 -8, i32 -16>
   ret <4 x i32> %1