InstCombine: Fix assert when reassociating fsub with undef

There is logic to track the expected number of instructions
produced. It thought in this case an instruction would
be necessary to negate the result, but here it folded
into a ConstantExpr fneg when the non-undef value operand
was cancelled out by the second fsub.

I'm not sure why we don't fold constant FP ops with undef currently,
but I think that would also avoid this problem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301199 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 05f34e9eaa0a3862a7154af1a5b59e3f3b87741d..e946acf84f5766dcfae632f9c43f2b8d3a5c1bcd 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -794,6 +794,11 @@ unsigned FAddCombine::calcInstrNumber(const AddendVect &Opnds) {
     if (Opnd->isConstant())
       continue;
 
+    // The constant check above is really for a few special constant
+    // coefficients.
+    if (isa<UndefValue>(Opnd->getSymVal()))
+      continue;
+
     const FAddendCoef &CE = Opnd->getCoef();
     if (CE.isMinusOne() || CE.isMinusTwo())
       NegOpndNum++;

diff --git a/test/Transforms/InstCombine/fsub.ll b/test/Transforms/InstCombine/fsub.ll
index af2fadd2867bc95c359615259cf011f180076fb8..6b62f5dd7e3899f8890d4ac380dd4d92da8f1869 100644 (file)
--- a/test/Transforms/InstCombine/fsub.ll
+++ b/test/Transforms/InstCombine/fsub.ll
@@ -21,3 +21,47 @@ define double @test2(double %x, double %y) nounwind {
 
   ret double %t2
 }
+
+; CHECK-LABEL: @fsub_undef(
+; CHECK: %sub = fsub float %val, undef
+define float @fsub_undef(float %val) {
+bb:
+  %sub = fsub float %val, undef
+  ret float %sub
+}
+
+; XXX - Why doesn't this fold to undef?
+; CHECK-LABEL: @fsub_fast_undef(
+; CHCK: %sub = fsub fast float %val, undef
+define float @fsub_fast_undef(float %val) {
+bb:
+  %sub = fsub fast float %val, undef
+  ret float %sub
+}
+
+; CHECK-LABEL: @fneg_undef(
+; CHECK: ret float fsub (float -0.000000e+00, float undef)
+define float @fneg_undef(float %val) {
+bb:
+  %sub = fsub float -0.0, undef
+  ret float %sub
+}
+
+; CHECK-LABEL: @fneg_fast_undef(
+; CHECK: ret float fsub (float -0.000000e+00, float undef)
+define float @fneg_fast_undef(float %val) {
+bb:
+  %sub = fsub fast float -0.0, undef
+  ret float %sub
+}
+
+; This folds to a constant expression, which produced 0 instructions
+; contrary to the expected one for negation.
+; CHECK-LABEL: @inconsistent_numbers_fsub_undef(
+; CHECK: ret float fsub (float -0.000000e+00, float undef)
+define float @inconsistent_numbers_fsub_undef(float %val) {
+bb:
+  %sub0 = fsub fast float %val, undef
+  %sub1 = fsub fast float %sub0, %val
+  ret float %sub1
+}