[InstCombine] fold fadd+fsub with common operand

rotateright · rotateright · commit fe839695a8b9 · 2018-08-08T16:19:22.000Z
This is a sibling to the simplify from: https://reviews.llvm.org/rL339174 llvm-svn: 339267
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1911,6 +1911,11 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
     if (match(Op0, m_FSub(m_Specific(Op1), m_Value(X))))
       return BinaryOperator::CreateFNegFMF(X, &I);
 
+    // Y - (X + Y) --> -X
+    // Y - (Y + X) --> -X
+    if (match(Op1, m_c_FAdd(m_Specific(Op0), m_Value(X))))
+      return BinaryOperator::CreateFNegFMF(X, &I);
+
     // TODO: This performs reassociative folds for FP ops. Some fraction of the
     // functionality has been subsumed by simple pattern matching here and in
     // InstSimplify. We should let a dedicated reassociation pass handle more
diff --git a/llvm/test/Transforms/InstCombine/fast-math.ll b/llvm/test/Transforms/InstCombine/fast-math.ll
@@ -269,8 +269,8 @@ define float @fold8_reassoc(float %f1) {
 
 define float @fsub_fadd_common_op_fneg(float %x, float %y) {
 ; CHECK-LABEL: @fsub_fadd_common_op_fneg(
-; CHECK-NEXT:    [[TMP1:%.*]] = fsub fast float -0.000000e+00, [[X:%.*]]
-; CHECK-NEXT:    ret float [[TMP1]]
+; CHECK-NEXT:    [[R:%.*]] = fsub fast float -0.000000e+00, [[X:%.*]]
+; CHECK-NEXT:    ret float [[R]]
 ;
   %a = fadd float %x, %y
   %r = fsub fast float %y, %a
@@ -283,8 +283,8 @@ define float @fsub_fadd_common_op_fneg(float %x, float %y) {
 
 define float @fsub_fadd_common_op_fneg_reassoc_nsz(float %x, float %y) {
 ; CHECK-LABEL: @fsub_fadd_common_op_fneg_reassoc_nsz(
-; CHECK-NEXT:    [[TMP1:%.*]] = fsub reassoc nsz float -0.000000e+00, [[X:%.*]]
-; CHECK-NEXT:    ret float [[TMP1]]
+; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz float -0.000000e+00, [[X:%.*]]
+; CHECK-NEXT:    ret float [[R]]
 ;
   %a = fadd float %x, %y
   %r = fsub reassoc nsz float %y, %a
@@ -295,8 +295,7 @@ define float @fsub_fadd_common_op_fneg_reassoc_nsz(float %x, float %y) {
 
 define <2 x float> @fsub_fadd_common_op_fneg_vec(<2 x float> %x, <2 x float> %y) {
 ; CHECK-LABEL: @fsub_fadd_common_op_fneg_vec(
-; CHECK-NEXT:    [[A:%.*]] = fadd <2 x float> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz <2 x float> [[Y]], [[A]]
+; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz <2 x float> <float -0.000000e+00, float -0.000000e+00>, [[X:%.*]]
 ; CHECK-NEXT:    ret <2 x float> [[R]]
 ;
   %a = fadd <2 x float> %x, %y
@@ -309,8 +308,8 @@ define <2 x float> @fsub_fadd_common_op_fneg_vec(<2 x float> %x, <2 x float> %y)
 
 define float @fsub_fadd_common_op_fneg_commute(float %x, float %y) {
 ; CHECK-LABEL: @fsub_fadd_common_op_fneg_commute(
-; CHECK-NEXT:    [[TMP1:%.*]] = fsub reassoc nsz float -0.000000e+00, [[X:%.*]]
-; CHECK-NEXT:    ret float [[TMP1]]
+; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz float -0.000000e+00, [[X:%.*]]
+; CHECK-NEXT:    ret float [[R]]
 ;
   %a = fadd float %y, %x
   %r = fsub reassoc nsz float %y, %a
@@ -321,8 +320,7 @@ define float @fsub_fadd_common_op_fneg_commute(float %x, float %y) {
 
 define <2 x float> @fsub_fadd_common_op_fneg_commute_vec(<2 x float> %x, <2 x float> %y) {
 ; CHECK-LABEL: @fsub_fadd_common_op_fneg_commute_vec(
-; CHECK-NEXT:    [[A:%.*]] = fadd <2 x float> [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz <2 x float> [[Y]], [[A]]
+; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz <2 x float> <float -0.000000e+00, float -0.000000e+00>, [[X:%.*]]
 ; CHECK-NEXT:    ret <2 x float> [[R]]
 ;
   %a = fadd <2 x float> %y, %x
