commit 85cba3b6fb4b797d26a16fefb6611c796a71cd1c
author Sanjay Patel <spatel@rotateright.com> Wed Oct 31 14:57:23 2018 +0000
committer Sanjay Patel <spatel@rotateright.com> Wed Oct 31 14:57:23 2018 +0000
tree fad9bfae0d72067f2eef9aba810b9364188dedab
parent 7d6d9eb6889c3f78a4466488d03744e408f39f1c

[InstSimplify] fold 'fcmp nnan oge X, 0.0' when X is not negative

This re-raises some of the open questions about how to apply and use fast-math-flags in IR from PR38086:
https://bugs.llvm.org/show_bug.cgi?id=38086
...but given the current implementation (no FMF on casts), this is likely the only way to predicate the 
transform.

This is part of solving PR39475:
https://bugs.llvm.org/show_bug.cgi?id=39475

Differential Revision: https://reviews.llvm.org/D53874

llvm-svn: 345725

llvm/lib/Analysis/InstructionSimplify.cpp

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index b138193..efe8850 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3612,6 +3612,10 @@
     }
     if (C->isZero()) {
       switch (Pred) {
+      case FCmpInst::FCMP_OGE:
+        if (FMF.noNaNs() && CannotBeOrderedLessThanZero(LHS, Q.TLI))
+          return getTrue(RetTy);
+        break;
       case FCmpInst::FCMP_UGE:
         if (CannotBeOrderedLessThanZero(LHS, Q.TLI))
           return getTrue(RetTy);

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index d7af4b8..d3702a4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -5433,8 +5433,8 @@
         break;
       // fabs(x) < 0 --> false
       case FCmpInst::FCMP_OLT:
-        llvm_unreachable("handled by SimplifyFCmpInst");
-      // fabs(x) > 0 --> x != 0
+        llvm_unreachable("fcmp should have simplified");
+          // fabs(x) > 0 --> x != 0
       case FCmpInst::FCMP_OGT:
         return new FCmpInst(FCmpInst::FCMP_ONE, CI->getArgOperand(0), RHSC);
       // fabs(x) <= 0 --> x == 0
@@ -5442,6 +5442,7 @@
         return new FCmpInst(FCmpInst::FCMP_OEQ, CI->getArgOperand(0), RHSC);
       // fabs(x) >= 0 --> !isnan(x)
       case FCmpInst::FCMP_OGE:
+        assert(!I.hasNoNaNs() && "fcmp should have simplified");
         return new FCmpInst(FCmpInst::FCMP_ORD, CI->getArgOperand(0), RHSC);
       // fabs(x) == 0 --> x == 0
       // fabs(x) != 0 --> x != 0