[PATCH] GVN: propagate fcmp equalities (PR17713)

[Sanjay Patel]

Hi reames, pete, ArchDRobison, hfinkel,

Patch based on suggestion in PR17713 ( http://llvm.org/bugs/show_bug.cgi?id=17713 ) and discussion in http://lists.cs.uiuc.edu/pipermail/llvmdev/2015-January/080314.html .

This just handles the simple case of propagating FP values along edges; there are still a lot of other cases (eg http://llvm.org/bugs/show_bug.cgi?id=17683 ) that need work.

http://reviews.llvm.org/D6911

Files:
  lib/Transforms/Scalar/GVN.cpp
  test/Transforms/GVN/edge.ll

Index: lib/Transforms/Scalar/GVN.cpp
===================================================================
--- lib/Transforms/Scalar/GVN.cpp
+++ lib/Transforms/Scalar/GVN.cpp
@@ -2171,15 +2171,20 @@
     // If we are propagating an equality like "(A == B)" == "true" then also
     // propagate the equality A == B.  When propagating a comparison such as
     // "(A >= B)" == "true", replace all instances of "A < B" with "false".
-    if (ICmpInst *Cmp = dyn_cast<ICmpInst>(LHS)) {
+    if (CmpInst *Cmp = dyn_cast<CmpInst>(LHS)) {
       Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1);
 
       // If "A == B" is known true, or "A != B" is known false, then replace
       // A with B everywhere in the scope.
       if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) ||
           (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE))
         Worklist.push_back(std::make_pair(Op0, Op1));
 
+      // Handle the floating point versions of equality comparisons too.
+      if ((isKnownTrue && Cmp->getPredicate() == CmpInst::FCMP_OEQ) ||
+          (isKnownFalse && Cmp->getPredicate() == CmpInst::FCMP_UNE))
+        Worklist.push_back(std::make_pair(Op0, Op1));
+
       // If "A >= B" is known true, replace "A < B" with false everywhere.
       CmpInst::Predicate NotPred = Cmp->getInversePredicate();
       Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse);
Index: test/Transforms/GVN/edge.ll
===================================================================
--- test/Transforms/GVN/edge.ll
+++ test/Transforms/GVN/edge.ll
@@ -58,3 +58,38 @@
 ; CHECK: call void @g(i1 %y)
   ret void
 }
+
+define double @fcmp_oeq(double %x, double %y) {
+entry:
+  %cmp = fcmp oeq double %y, 2.000000e+00
+  br i1 %cmp, label %if, label %return
+
+if:
+  %div = fdiv double %x, %y
+  br label %return
+
+return:
+  %retval.0 = phi double [ %div, %if ], [ %x, %entry ]
+  ret double %retval.0
+
+; CHECK-LABEL: define double @fcmp_oeq(
+; CHECK: %div = fdiv double %x, 2.000000e+00
+}
+
+define double @fcmp_une(double %x, double %y) {
+entry:
+  %cmp = fcmp une double %y, 2.000000e+00
+  br i1 %cmp, label %return, label %else
+
+else:
+  %div = fdiv double %x, %y
+  br label %return
+
+return:
+  %retval.0 = phi double [ %div, %else ], [ %x, %entry ]
+  ret double %retval.0
+
+; CHECK-LABEL: define double @fcmp_une(
+; CHECK: %div = fdiv double %x, 2.000000e+00
+}
+

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