Make this transformation slightly less agressive and more correct.

The 'CmpInst::isFalseWhenEqual' function returns 'false' for values other than
simply equality. For instance, it returns 'false' for <= or >=. This isn't the
correct behavior for this transformation, which is checking for strict equality
and non-equality. It was causing the gcc.c-torture/execute/frame-address.c test
to fail because it would completely (and incorrectly) optimize a whole function
into a 'ret i32 0'.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152497 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 53 insertions, 8 deletions

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index c024e9260b..95fd48ee65 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1609,23 +1609,33 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     if (llvm::isKnownNonNull(LHSPtr) || llvm::isKnownNonNull(RHSPtr)) {
       // If both sides are different identified objects, they aren't equal
       // unless they're null.
-      if (LHSPtr != RHSPtr && llvm::isIdentifiedObject(RHSPtr))
-        return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
+      if (LHSPtr != RHSPtr && llvm::isIdentifiedObject(RHSPtr) &&
+          (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::FCMP_UEQ))
+        return ConstantInt::get(ITy, false);
 
       // A local identified object (alloca or noalias call) can't equal any
       // incoming argument, unless they're both null.
-      if (isa<Instruction>(LHSPtr) && isa<Argument>(RHSPtr))
-        return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
+      if (isa<Instruction>(LHSPtr) && isa<Argument>(RHSPtr) &&
+          (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::FCMP_UEQ))
+        return ConstantInt::get(ITy, false);
     }
 
     // Assume that the constant null is on the right.
-    if (llvm::isKnownNonNull(LHSPtr) && isa<ConstantPointerNull>(RHSPtr))
-      return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
+    if (llvm::isKnownNonNull(LHSPtr) && isa<ConstantPointerNull>(RHSPtr)) {
+      if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::FCMP_UEQ)
+        return ConstantInt::get(ITy, false);
+      else if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::FCMP_ONE)
+        return ConstantInt::get(ITy, true);
+    }
   } else if (isa<Argument>(LHSPtr)) {
     RHSPtr = RHSPtr->stripInBoundsOffsets();
     // An alloca can't be equal to an argument.
-    if (isa<AllocaInst>(RHSPtr))
-      return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
+    if (isa<AllocaInst>(RHSPtr)) {
+      if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::FCMP_UEQ)
+        return ConstantInt::get(ITy, false);
+      else if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::FCMP_ONE)
+        return ConstantInt::get(ITy, true);
+    }
   }
 
   // If we are comparing with zero then try hard since this is a common case.
diff --git a/test/Transforms/InstCombine/2012-03-10-InstCombine.ll b/test/Transforms/InstCombine/2012-03-10-InstCombine.ll
new file mode 100644
index 0000000000..6898997254
--- /dev/null
+++ b/test/Transforms/InstCombine/2012-03-10-InstCombine.ll
@@ -0,0 +1,35 @@
+; RUN: opt < %s -instcombine | FileCheck %s
+
+; Derived from gcc.c-torture/execute/frame-address.c
+
+; CHECK:     @func
+; CHECK:     return:
+; CHECK-NOT: ret i32 0
+; CHECK:     ret i32 %retval
+
+define i32 @func(i8* %c, i8* %f) nounwind uwtable readnone noinline ssp {
+entry:
+  %d = alloca i8, align 1
+  store i8 0, i8* %d, align 1
+  %cmp = icmp ugt i8* %d, %c
+  br i1 %cmp, label %if.else, label %if.then
+
+if.then:                                          ; preds = %entry
+  %cmp2 = icmp ule i8* %d, %f
+  %not.cmp1 = icmp uge i8* %c, %f
+  %.cmp2 = and i1 %cmp2, %not.cmp1
+  %land.ext = zext i1 %.cmp2 to i32
+  br label %return
+
+if.else:                                          ; preds = %entry
+  %cmp5 = icmp uge i8* %d, %f
+  %not.cmp3 = icmp ule i8* %c, %f
+  %.cmp5 = and i1 %cmp5, %not.cmp3
+  %land.ext7 = zext i1 %.cmp5 to i32
+  br label %return
+
+return:                                           ; preds = %if.else, %if.then
+  %retval.0 = phi i32 [ %land.ext, %if.then ], [ %land.ext7, %if.else ]
+  ret i32 %retval.0
+}
+