Fixed the lost FastMathFlags in GVN(Global Value Numbering).

Reviewer: Hal Finkel.
Differential Revision: https://reviews.llvm.org/D26952

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287700 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index b6591531265cd630ed1e0c26efabc4b372b12cf7..d5234c0f7e3271134b4ff14ee125cbb67c64068d 100644 (file)
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -1731,7 +1731,12 @@ static void patchReplacementInstruction(Instruction *I, Value *Repl) {
 
   // Patch the replacement so that it is not more restrictive than the value
   // being replaced.
-  ReplInst->andIRFlags(I);
+  // Note that if 'I' is a load being replaced by some operation, 
+  // for example, by an arithmetic operation, then andIRFlags()
+  // would just erase all math flags from the original arithmetic
+  // operation, which is clearly not wanted and not needed.
+  if (!isa<LoadInst>(I))
+    ReplInst->andIRFlags(I);
 
   // FIXME: If both the original and replacement value are part of the
   // same control-flow region (meaning that the execution of one

diff --git a/test/Transforms/GVN/propagate-ir-flags.ll b/test/Transforms/GVN/propagate-ir-flags.ll
new file mode 100644 (file)
index 0000000..07367a2
--- /dev/null
+++ b/test/Transforms/GVN/propagate-ir-flags.ll
@@ -0,0 +1,29 @@
+
+; RUN: opt < %s -gvn -S | FileCheck %s
+
+; CHECK-LABEL: func_fast
+; CHECK:       fadd fast double
+; CHECK-NEXT:  store
+; CHECK-NEXT:  ret
+define double @func_fast(double %a, double %b) {
+entry:
+  %a.addr = alloca double, align 8
+  %add = fadd fast double %b, 3.000000e+00
+  store double %add, double* %a.addr, align 8
+  %load_add = load double, double* %a.addr, align 8
+  ret double %load_add
+}
+
+; CHECK-LABEL: func_no_fast
+; CHECK:       fadd double
+; CHECK-NEXT:  store
+; CHECK-NEXT:  ret
+define double @func_no_fast(double %a, double %b) {
+entry:
+  %a.addr = alloca double, align 8
+  %add = fadd fast double %b, 3.000000e+00
+  store double %add, double* %a.addr, align 8
+  %duplicated_add = fadd double %b, 3.000000e+00
+  ret double %duplicated_add
+}
+