Generalize icmp matching in IndVars' eliminateTrunc

We were only matching RHS being a loop invariant value, not the inverse. Since there's nothing which appears to canonicalize loop invariant values to RHS, this means we missed cases.

Differential Revision: https://reviews.llvm.org/D63112

llvm-svn: 363108

1 files changed, 15 insertions, 14 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 9a4ebd3..f1048d9 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -521,20 +521,19 @@ bool SimplifyIndvar::eliminateTrunc(TruncInst *TI) {
     if (isa<Instruction>(U) &&
         !DT->isReachableFromEntry(cast<Instruction>(U)->getParent()))
       continue;
-    if (ICmpInst *ICI = dyn_cast<ICmpInst>(U)) {
-      if (ICI->getOperand(0) == TI && L->isLoopInvariant(ICI->getOperand(1))) {
-        assert(L->contains(ICI->getParent()) && "LCSSA form broken?");
-        // If we cannot get rid of trunc, bail.
-        if (ICI->isSigned() && !DoesSExtCollapse)
-          return false;
-        if (ICI->isUnsigned() && !DoesZExtCollapse)
-          return false;
-        // For equality, either signed or unsigned works.
-        ICmpUsers.push_back(ICI);
-      } else
-        return false;
-    } else
+    ICmpInst *ICI = dyn_cast<ICmpInst>(U);
+    if (!ICI) return false;
+    assert(L->contains(ICI->getParent()) && "LCSSA form broken?");
+    if (!(ICI->getOperand(0) == TI && L->isLoopInvariant(ICI->getOperand(1))) &&
+        !(ICI->getOperand(1) == TI && L->isLoopInvariant(ICI->getOperand(0))))
       return false;
+    // If we cannot get rid of trunc, bail.
+    if (ICI->isSigned() && !DoesSExtCollapse)
+      return false;
+    if (ICI->isUnsigned() && !DoesZExtCollapse)
+      return false;
+    // For equality, either signed or unsigned works.
+    ICmpUsers.push_back(ICI);
   }
 
   auto CanUseZExt = [&](ICmpInst *ICI) {
@@ -557,7 +556,8 @@ bool SimplifyIndvar::eliminateTrunc(TruncInst *TI) {
   };
   // Replace all comparisons against trunc with comparisons against IV.
   for (auto *ICI : ICmpUsers) {
-    auto *Op1 = ICI->getOperand(1);
+    bool IsSwapped = L->isLoopInvariant(ICI->getOperand(0));
+    auto *Op1 = IsSwapped ? ICI->getOperand(0) : ICI->getOperand(1);
     Instruction *Ext = nullptr;
     // For signed/unsigned predicate, replace the old comparison with comparison
     // of immediate IV against sext/zext of the invariant argument. If we can
@@ -566,6 +566,7 @@ bool SimplifyIndvar::eliminateTrunc(TruncInst *TI) {
     // TODO: If we see a signed comparison which can be turned into unsigned,
     // we can do it here for canonicalization purposes.
     ICmpInst::Predicate Pred = ICI->getPredicate();
+    if (IsSwapped) Pred = ICmpInst::getSwappedPredicate(Pred);
     if (CanUseZExt(ICI)) {
       assert(DoesZExtCollapse && "Unprofitable zext?");
       Ext = new ZExtInst(Op1, IVTy, "zext", ICI);