[IR] Add a dedicated FNeg IR Instruction

The IEEE-754 Standard makes it clear that fneg(x) and
fsub(-0.0, x) are two different operations. The former is a bitwise
operation, while the latter is an arithmetic operation. This patch
creates a dedicated FNeg IR Instruction to model that behavior.

Differential Revision: https://reviews.llvm.org/D53877

llvm-svn: 346774

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/Generic/fneg-fabs.ll b/llvm/test/CodeGen/Generic/fneg-fabs.ll
index 2f2f59762cb..cafc1f132b5 100644
--- a/llvm/test/CodeGen/Generic/fneg-fabs.ll
+++ b/llvm/test/CodeGen/Generic/fneg-fabs.ll
@@ -10,6 +10,21 @@ define float @fnegf(float %X) {
         ret float %Y
 }
 
+define double @real_fneg(double %X) {
+        %Y = fneg double %X               ; <double> [#uses=1]
+        ret double %Y
+}
+
+define double @real_fneg_constant() {
+        %Y = fneg double -2.0             ; <double> [#uses=1]
+        ret double %Y
+}
+
+define float @real_fnegf(float %X) {
+        %Y = fneg float %X                ; <float> [#uses=1]
+        ret float %Y
+}
+
 declare double @fabs(double)
 
 declare float @fabsf(float)