[EarlyCSE] recognize commuted and swapped variants of min/max as equivalent (PR35642)

As shown in:
https://bugs.llvm.org/show_bug.cgi?id=35642
...we can have different forms of min/max, so we should recognize those here in EarlyCSE 
similar to how we already handle binops and compares that can commute.

Differential Revision: https://reviews.llvm.org/D41136

llvm-svn: 320640

1 files changed, 27 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index 1066dc33007..11bf8ee733c 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -27,6 +27,7 @@
 #include "llvm/Analysis/MemorySSAUpdater.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
@@ -142,6 +143,19 @@ unsigned DenseMapInfo<SimpleValue>::getHashValue(SimpleValue Val) {
     return hash_combine(Inst->getOpcode(), Pred, LHS, RHS);
   }
 
+  // Hash min/max (cmp + select) to allow for commuted operands, non-canonical
+  // compare predicate (eg, the compare for smin may use 'sgt' rather than
+  // 'slt'), and non-canonical operands in the compare.
+  Value *A, *B;
+  SelectPatternFlavor SPF = matchSelectPattern(Inst, A, B).Flavor;
+  // TODO: We should also detect abs and FP min/max.
+  if (SPF == SPF_SMIN || SPF == SPF_SMAX ||
+      SPF == SPF_UMIN || SPF == SPF_UMAX) {
+    if (A > B)
+      std::swap(A, B);
+    return hash_combine(Inst->getOpcode(), SPF, A, B);
+  }
+
   if (CastInst *CI = dyn_cast<CastInst>(Inst))
     return hash_combine(CI->getOpcode(), CI->getType(), CI->getOperand(0));
 
@@ -200,6 +214,19 @@ bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) {
            LHSCmp->getSwappedPredicate() == RHSCmp->getPredicate();
   }
 
+  // Min/max can occur with commuted operands, non-canonical predicates, and/or
+  // non-canonical operands.
+  Value *LHSA, *LHSB;
+  SelectPatternFlavor LSPF = matchSelectPattern(LHSI, LHSA, LHSB).Flavor;
+  // TODO: We should also detect abs and FP min/max.
+  if (LSPF == SPF_SMIN || LSPF == SPF_SMAX ||
+      LSPF == SPF_UMIN || LSPF == SPF_UMAX) {
+    Value *RHSA, *RHSB;
+    SelectPatternFlavor RSPF = matchSelectPattern(RHSI, RHSA, RHSB).Flavor;
+    return (LSPF == RSPF && ((LHSA == RHSA && LHSB == RHSB) ||
+                             (LHSA == RHSB && LHSB == RHSA)));
+  }
+
   return false;
 }