[llvm] r367227 - [InstCombine] fold fadd+fneg with fdiv/fmul betweena

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Mon Jul 29 06:50:25 2019
New Revision: 367227

URL: http://llvm.org/viewvc/llvm-project?rev=367227&view=rev
Log:
[InstCombine] fold fadd+fneg with fdiv/fmul betweena

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/fadd.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp?rev=367227&r1=367226&r2=367227&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp Mon Jul 29 06:50:25 2019
@@ -1387,6 +1387,24 @@ Instruction *InstCombiner::visitFAdd(Bin
   if (match(&I, m_c_FAdd(m_FNeg(m_Value(X)), m_Value(Y))))
     return BinaryOperator::CreateFSubFMF(Y, X, &I);
 
+  // Similar to above, but look through fmul/fdiv for the negated term.
+  // (-X * Y) + Z --> Z - (X * Y) [4 commuted variants]
+  Value *Z;
+  if (match(&I, m_c_FAdd(m_OneUse(m_c_FMul(m_FNeg(m_Value(X)), m_Value(Y))),
+                         m_Value(Z)))) {
+    Value *XY = Builder.CreateFMulFMF(X, Y, &I);
+    return BinaryOperator::CreateFSubFMF(Z, XY, &I);
+  }
+  // (-X / Y) + Z --> Z - (X / Y) [2 commuted variants]
+  // (X / -Y) + Z --> Z - (X / Y) [2 commuted variants]
+  if (match(&I, m_c_FAdd(m_OneUse(m_FDiv(m_FNeg(m_Value(X)), m_Value(Y))),
+                         m_Value(Z))) ||
+      match(&I, m_c_FAdd(m_OneUse(m_FDiv(m_Value(X), m_FNeg(m_Value(Y)))),
+                         m_Value(Z)))) {
+    Value *XY = Builder.CreateFDivFMF(X, Y, &I);
+    return BinaryOperator::CreateFSubFMF(Z, XY, &I);
+  }
+
   // Check for (fadd double (sitofp x), y), see if we can merge this into an
   // integer add followed by a promotion.
   Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);

Modified: llvm/trunk/test/Transforms/InstCombine/fadd.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fadd.ll?rev=367227&r1=367226&r2=367227&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/fadd.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/fadd.ll Mon Jul 29 06:50:25 2019
@@ -246,8 +246,8 @@ define float @fdiv_fneg1_extra_use2(floa
 ; CHECK-LABEL: @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:%.*]] = fadd float [[DIV]], [[Z:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fdiv float [[X]], [[Y:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = fsub float [[Z:%.*]], [[TMP1]]
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %neg = fsub float -0.000000e+00, %x
@@ -263,8 +263,8 @@ define float @fdiv_fneg2_extra_use2(floa
 ; CHECK-LABEL: @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:%.*]] = fadd float [[DIV]], [[Z:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fdiv float [[Y:%.*]], [[X]]
+; CHECK-NEXT:    [[R:%.*]] = fsub float [[Z:%.*]], [[TMP1]]
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %neg = fsub float -0.000000e+00, %x
@@ -280,8 +280,8 @@ define <2 x float> @fmul_fneg1_extra_use
 ; CHECK-LABEL: @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:%.*]] = fadd <2 x float> [[MUL]], [[Z:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fmul <2 x float> [[X]], [[Y:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = fsub <2 x float> [[Z:%.*]], [[TMP1]]
 ; CHECK-NEXT:    ret <2 x float> [[R]]
 ;
   %neg = fsub <2 x float> <float -0.0, float -0.0>, %x
@@ -298,8 +298,8 @@ define float @fmul_fneg2_extra_use2(floa
 ; CHECK-NEXT:    [[Y:%.*]] = frem float -4.200000e+01, [[PY:%.*]]
 ; CHECK-NEXT:    [[NEG:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[NEG]])
-; CHECK-NEXT:    [[MUL:%.*]] = fmul float [[Y]], [[NEG]]
-; CHECK-NEXT:    [[R:%.*]] = fadd float [[MUL]], [[Z:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fmul float [[Y]], [[X]]
+; CHECK-NEXT:    [[R:%.*]] = fsub float [[Z:%.*]], [[TMP1]]
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %y = frem float -42.0, %py ; thwart complexity-based canonicalization