[ValueTracking, InstCombine] canonicalize fcmp ord/uno with non-NAN ops to null constants

This is a preliminary step towards solving the remaining part of PR27145 - IR for isfinite():
https://bugs.llvm.org/show_bug.cgi?id=27145

In order to solve that one more generally, we need to add matching for and/or of fcmp ord/uno
with a constant operand.

But while looking at those patterns, I realized we were missing a canonicalization for nonzero
constants. Rather than limiting to just folds for constants, we're adding a general value
tracking method for this based on an existing DAG helper.

By transforming everything to 0.0, we can simplify the existing code in foldLogicOfFCmps()
and pick up missing vector folds.

Differential Revision: https://reviews.llvm.org/D37427

llvm-svn: 312591

1 files changed, 6 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 006ed418c73..a81f295b91d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -938,21 +938,12 @@ Value *InstCombiner::foldLogicOfFCmps(FCmpInst *LHS, FCmpInst *RHS, bool IsAnd)
     if (LHS0->getType() != RHS0->getType())
       return nullptr;
 
-    auto *LHSC = dyn_cast<ConstantFP>(LHS1);
-    auto *RHSC = dyn_cast<ConstantFP>(RHS1);
-    if (LHSC && RHSC) {
-      assert(!LHSC->getValueAPF().isNaN() && !RHSC->getValueAPF().isNaN() &&
-             "Failed to simplify fcmp ord/uno with NAN operand");
-      // Ignore the constants because they can't be NANs:
-      // (fcmp ord x, c) & (fcmp ord y, c)  -> (fcmp ord x, y)
-      // (fcmp uno x, c) & (fcmp uno y, c)  -> (fcmp uno x, y)
-      return Builder.CreateFCmp(PredL, LHS0, RHS0);
-    }
-
-    // Handle vector zeros. This occurs because the canonical form of
-    // "fcmp ord/uno x,x" is "fcmp ord/uno x, 0".
-    if (isa<ConstantAggregateZero>(LHS1) &&
-        isa<ConstantAggregateZero>(RHS1))
+    // FCmp canonicalization ensures that (fcmp ord/uno X, X) and
+    // (fcmp ord/uno X, C) will be transformed to (fcmp X, 0.0).
+    if (match(LHS1, m_Zero()) && LHS1 == RHS1)
+      // Ignore the constants because they are obviously not NANs:
+      // (fcmp ord x, 0.0) & (fcmp ord y, 0.0)  -> (fcmp ord x, y)
+      // (fcmp uno x, 0.0) | (fcmp uno y, 0.0)  -> (fcmp uno x, y)
       return Builder.CreateFCmp(PredL, LHS0, RHS0);
   }