[APFloat] Fixed a bug in method 'fusedMultiplyAdd'.

When folding a fused multiply-add builtin call, make sure that we propagate the
correct result in the case where the addend is zero, and the two other operands
are finite non-zero.

Example:
  define double @test() {
    %1 = call double @llvm.fma.f64(double 7.0, double 8.0, double 0.0)
    ret double %1
  }

Before this patch, the instruction simplifier wrongly folded the builtin call
in function @test to constant 'double 7.0'.
With this patch, method 'fusedMultiplyAdd' correctly evaluates the multiply and
propagates the expected result (i.e. 56.0).

Added test fold-builtin-fma.ll with the reproducible from PR20832 plus extra
test cases to verify the behavior of method 'fusedMultiplyAdd' in the presence
of NaN/Inf operands.

This fixes PR20832.

Differential Revision: http://reviews.llvm.org/D5152

llvm-svn: 216913

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
index 7989e30afae..ab641fdbe79 100644
--- a/llvm/lib/Support/APFloat.cpp
+++ b/llvm/lib/Support/APFloat.cpp
@@ -1801,7 +1801,7 @@ APFloat::fusedMultiplyAdd(const APFloat &multiplicand,
      extended-precision calculation.  */
   if (isFiniteNonZero() &&
       multiplicand.isFiniteNonZero() &&
-      addend.isFiniteNonZero()) {
+      addend.isFinite()) {
     lostFraction lost_fraction;
 
     lost_fraction = multiplySignificand(multiplicand, &addend);