[llvm] r367194 - [InstCombine] fold fsub+fneg with fdiv/fmul between

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Sun Jul 28 10:10:06 2019
New Revision: 367194

URL: http://llvm.org/viewvc/llvm-project?rev=367194&view=rev
Log:
[InstCombine] fold fsub+fneg with fdiv/fmul between

The backend already does this via isNegatibleForFree(),
but we may want to alter the fneg IR canonicalizations
that currently exist, so we need to try harder to fold
fneg in IR to avoid regressions.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    llvm/trunk/test/Transforms/InstCombine/fsub.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp?rev=367194&r1=367193&r2=367194&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp Sun Jul 28 10:10:06 2019
@@ -1964,6 +1964,21 @@ Instruction *InstCombiner::visitFSub(Bin
   if (match(Op1, m_OneUse(m_FPExt(m_FNeg(m_Value(Y))))))
     return BinaryOperator::CreateFAddFMF(Op0, Builder.CreateFPExt(Y, Ty), &I);
 
+  // Similar to above, but look through fmul/fdiv of the negated value:
+  // Op0 - (-X * Y) --> Op0 + (X * Y)
+  // Op0 - (Y * -X) --> Op0 + (X * Y)
+  if (match(Op1, m_OneUse(m_c_FMul(m_FNeg(m_Value(X)), m_Value(Y))))) {
+    Value *FMul = Builder.CreateFMulFMF(X, Y, &I);
+    return BinaryOperator::CreateFAddFMF(Op0, FMul, &I);
+  }
+  // Op0 - (-X / Y) --> Op0 + (X / Y)
+  // Op0 - (X / -Y) --> Op0 + (X / Y)
+  if (match(Op1, m_OneUse(m_FDiv(m_FNeg(m_Value(X)), m_Value(Y)))) ||
+      match(Op1, m_OneUse(m_FDiv(m_Value(X), m_FNeg(m_Value(Y)))))) {
+    Value *FDiv = Builder.CreateFDivFMF(X, Y, &I);
+    return BinaryOperator::CreateFAddFMF(Op0, FDiv, &I);
+  }
+
   // Handle special cases for FSub with selects feeding the operation
   if (Value *V = SimplifySelectsFeedingBinaryOp(I, Op0, Op1))
     return replaceInstUsesWith(I, V);

Modified: llvm/trunk/test/Transforms/InstCombine/fsub.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fsub.ll?rev=367194&r1=367193&r2=367194&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/fsub.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/fsub.ll Sun Jul 28 10:10:06 2019
@@ -518,8 +518,8 @@ define float @fsub_fdiv_fneg1_extra_use2
 ; CHECK-LABEL: @fsub_fdiv_fneg1_extra_use2(
 ; CHECK-NEXT:    [[NEG:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[NEG]])
-; CHECK-NEXT:    [[DIV:%.*]] = fdiv float [[NEG]], [[Y:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = fsub float [[Z:%.*]], [[DIV]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fdiv float [[X]], [[Y:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = fadd float [[TMP1]], [[Z:%.*]]
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %neg = fsub float -0.000000e+00, %x
@@ -533,8 +533,8 @@ define float @fsub_fdiv_fneg2_extra_use2
 ; CHECK-LABEL: @fsub_fdiv_fneg2_extra_use2(
 ; CHECK-NEXT:    [[NEG:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[NEG]])
-; CHECK-NEXT:    [[DIV:%.*]] = fdiv float [[Y:%.*]], [[NEG]]
-; CHECK-NEXT:    [[R:%.*]] = fsub float [[Z:%.*]], [[DIV]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fdiv float [[Y:%.*]], [[X]]
+; CHECK-NEXT:    [[R:%.*]] = fadd float [[TMP1]], [[Z:%.*]]
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %neg = fsub float -0.000000e+00, %x
@@ -548,8 +548,8 @@ define <2 x float> @fsub_fmul_fneg1_extr
 ; CHECK-LABEL: @fsub_fmul_fneg1_extra_use2(
 ; CHECK-NEXT:    [[NEG:%.*]] = fsub <2 x float> <float -0.000000e+00, float -0.000000e+00>, [[X:%.*]]
 ; CHECK-NEXT:    call void @use_vec(<2 x float> [[NEG]])
-; CHECK-NEXT:    [[MUL:%.*]] = fmul <2 x float> [[NEG]], [[Y:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = fsub <2 x float> [[Z:%.*]], [[MUL]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fmul <2 x float> [[X]], [[Y:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = fadd <2 x float> [[TMP1]], [[Z:%.*]]
 ; CHECK-NEXT:    ret <2 x float> [[R]]
 ;
   %neg = fsub <2 x float> <float -0.0, float -0.0>, %x
@@ -563,8 +563,8 @@ define float @fsub_fmul_fneg2_extra_use2
 ; CHECK-LABEL: @fsub_fmul_fneg2_extra_use2(
 ; CHECK-NEXT:    [[NEG:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[NEG]])
-; CHECK-NEXT:    [[MUL:%.*]] = fmul float [[NEG]], [[Y:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = fsub float [[Z:%.*]], [[MUL]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fmul float [[X]], [[Y:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = fadd float [[TMP1]], [[Z:%.*]]
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %neg = fsub float -0.000000e+00, %x