[InstCombine] Update fptrunc (fneg x)) -> (fneg (fptrunc x) for unary FNeg

Differential Revision: https://reviews.llvm.org/D62629

llvm-svn: 363080

Author: mcinally

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -1615,12 +1615,20 @@ Instruction *InstCombiner::visitFPTrunc(FPTruncInst &FPT) {
         return CastInst::CreateFPCast(ExactResult, Ty);
       }
     }
+  }
 
-    // (fptrunc (fneg x)) -> (fneg (fptrunc x))
-    Value *X;
-    if (match(OpI, m_FNeg(m_Value(X)))) {
+  // (fptrunc (fneg x)) -> (fneg (fptrunc x))
+  Value *X;
+  Instruction *Op = dyn_cast<Instruction>(FPT.getOperand(0));
+  if (Op && Op->hasOneUse()) {
+    if (match(Op, m_FNeg(m_Value(X)))) {
       Value *InnerTrunc = Builder.CreateFPTrunc(X, Ty);
-      return BinaryOperator::CreateFNegFMF(InnerTrunc, OpI);
+
+      // FIXME: Once we're sure that unary FNeg optimizations are on par with
+      // binary FNeg, this should always return a unary operator.
+      if (isa<BinaryOperator>(Op))
+        return BinaryOperator::CreateFNegFMF(InnerTrunc, Op);
+      return UnaryOperator::CreateFNegFMF(InnerTrunc, Op);
     }
   }
 

llvm/test/Transforms/InstCombine/fpcast.ll

@@ -40,11 +40,10 @@ define half @fneg_fptrunc(float %a) {
   ret half %c
 }
 
-; FIXME: This combine isn't working.
 define half @unary_fneg_fptrunc(float %a) {
 ; CHECK-LABEL: @unary_fneg_fptrunc(
-; CHECK-NEXT:    [[B:%.*]] = fneg float [[A:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = fptrunc float [[B]] to half
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
+; CHECK-NEXT:    [[C:%.*]] = fneg half [[TMP1]]
 ; CHECK-NEXT:    ret half [[C]]
 ;
   %b = fneg float %a
@@ -63,11 +62,10 @@ define <2 x half> @fneg_fptrunc_vec_undef(<2 x float> %a) {
   ret <2 x half> %c
 }
 
-; FIXME: This combine isn't working.
 define <2 x half> @unary_fneg_fptrunc_vec(<2 x float> %a) {
 ; CHECK-LABEL: @unary_fneg_fptrunc_vec(
-; CHECK-NEXT:    [[B:%.*]] = fneg <2 x float> [[A:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = fptrunc <2 x float> [[B]] to <2 x half>
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc <2 x float> [[A:%.*]] to <2 x half>
+; CHECK-NEXT:    [[C:%.*]] = fneg <2 x half> [[TMP1]]
 ; CHECK-NEXT:    ret <2 x half> [[C]]
 ;
   %b = fneg <2 x float> %a
@@ -86,11 +84,10 @@ define half @test4-fast(float %a) {
   ret half %c
 }
 
-; FIXME: This combine isn't working.
 define half @test4_unary_fneg-fast(float %a) {
 ; CHECK-LABEL: @test4_unary_fneg-fast(
-; CHECK-NEXT:    [[B:%.*]] = fneg fast float [[A:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = fptrunc float [[B]] to half
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
+; CHECK-NEXT:    [[C:%.*]] = fneg fast half [[TMP1]]
 ; CHECK-NEXT:    ret half [[C]]
 ;
   %b = fneg fast float %a

llvm/test/Transforms/InstCombine/fpextend.ll

@@ -55,13 +55,10 @@ entry:
   ret float %tmp34
 }
 
-; FIXME: This combine isn't working.
 define float @test4_unary_fneg(float %x) nounwind  {
 ; CHECK-LABEL: @test4_unary_fneg(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP1:%.*]] = fpext float [[X:%.*]] to double
-; CHECK-NEXT:    [[TMP2:%.*]] = fneg double [[TMP1]]
-; CHECK-NEXT:    [[TMP34:%.*]] = fptrunc double [[TMP2]] to float
+; CHECK-NEXT:    [[TMP34:%.*]] = fneg float [[X:%.*]]
 ; CHECK-NEXT:    ret float [[TMP34]]
 ;
 entry:

llvm/test/Transforms/InstCombine/fsub.ll

@@ -345,12 +345,11 @@ define float @neg_trunc_op1_extra_use(double %a, float %b) {
   ret float %t3
 }
 
-; FIXME: This combine isn't working.
 define float @unary_neg_trunc_op1_extra_use(double %a, float %b) {
 ; CHECK-LABEL: @unary_neg_trunc_op1_extra_use(
-; CHECK-NEXT:    [[T1:%.*]] = fneg double [[A:%.*]]
-; CHECK-NEXT:    [[T2:%.*]] = fptrunc double [[T1]] to float
-; CHECK-NEXT:    [[T3:%.*]] = fsub float [[B:%.*]], [[T2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc double [[A:%.*]] to float
+; CHECK-NEXT:    [[T2:%.*]] = fneg float [[TMP1]]
+; CHECK-NEXT:    [[T3:%.*]] = fadd float [[TMP1]], [[B:%.*]]
 ; CHECK-NEXT:    call void @use(float [[T2]])
 ; CHECK-NEXT:    ret float [[T3]]
 ;