Handle some more combinations of extend and icmp. Fixes PR1940.

llvm-svn: 46431

2 files changed, 25 insertions, 8 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 5ba48572a5d..e56b5599717 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -5820,18 +5820,22 @@ Instruction *InstCombiner::visitICmpInstWithCastAndCast(ICmpInst &ICI) {
     if (RHSCIOp->getType() != LHSCIOp->getType()) 
       return 0;
     
-    // If the signedness of the two compares doesn't agree (i.e. one is a sext
+    // If the signedness of the two casts doesn't agree (i.e. one is a sext
     // and the other is a zext), then we can't handle this.
     if (CI->getOpcode() != LHSCI->getOpcode())
       return 0;
 
-    // Likewise, if the signedness of the [sz]exts and the compare don't match, 
-    // then we can't handle this.
-    if (isSignedExt != isSignedCmp && !ICI.isEquality())
-      return 0;
-    
-    // Okay, just insert a compare of the reduced operands now!
-    return new ICmpInst(ICI.getPredicate(), LHSCIOp, RHSCIOp);
+    // Deal with equality cases early.
+    if (ICI.isEquality())
+      return new ICmpInst(ICI.getPredicate(), LHSCIOp, RHSCIOp);
+
+    // A signed comparison of sign extended values simplifies into a
+    // signed comparison.
+    if (isSignedCmp && isSignedExt)
+      return new ICmpInst(ICI.getPredicate(), LHSCIOp, RHSCIOp);
+
+    // The other three cases all fold into an unsigned comparison.
+    return new ICmpInst(ICI.getUnsignedPredicate(), LHSCIOp, RHSCIOp);
   }
 
   // If we aren't dealing with a constant on the RHS, exit early
diff --git a/llvm/lib/VMCore/Instructions.cpp b/llvm/lib/VMCore/Instructions.cpp
index 156eff169c1..b945a5a0dd7 100644
--- a/llvm/lib/VMCore/Instructions.cpp
+++ b/llvm/lib/VMCore/Instructions.cpp
@@ -2429,6 +2429,19 @@ ICmpInst::Predicate ICmpInst::getSignedPredicate(Predicate pred) {
   }
 }
 
+ICmpInst::Predicate ICmpInst::getUnsignedPredicate(Predicate pred) {
+  switch (pred) {
+    default: assert(! "Unknown icmp predicate!");
+    case ICMP_EQ: case ICMP_NE: 
+    case ICMP_UGT: case ICMP_ULT: case ICMP_UGE: case ICMP_ULE: 
+       return pred;
+    case ICMP_SGT: return ICMP_UGT;
+    case ICMP_SLT: return ICMP_ULT;
+    case ICMP_SGE: return ICMP_UGE;
+    case ICMP_SLE: return ICMP_ULE;
+  }
+}
+
 bool ICmpInst::isSignedPredicate(Predicate pred) {
   switch (pred) {
     default: assert(! "Unknown icmp predicate!");