Aggressively flip compare constant expressions where appropriate; constant

folding in particular expects null to be on the RHS.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91587 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp
index 7f713d15c67a4f00dc30da0aada133324ab24f16..2449739aaf502c4b0aff8add82e84319a498d9c8 100644 (file)
--- a/lib/VMCore/ConstantFold.cpp
+++ b/lib/VMCore/ConstantFold.cpp
@@ -1839,14 +1839,16 @@ Constant *llvm::ConstantFoldCompareInstruction(LLVMContext &Context,
       }
     }
 
-    if (!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) {
+    if ((!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) ||
+        (C1->isNullValue() && !C2->isNullValue())) {
       // If C2 is a constant expr and C1 isn't, flip them around and fold the
       // other way if possible.
+      // Also, if C1 is null and C2 isn't, flip them around.
       switch (pred) {
       case ICmpInst::ICMP_EQ:
       case ICmpInst::ICMP_NE:
         // No change of predicate required.
-        return ConstantFoldCompareInstruction(Context, pred, C2, C1);
+        return ConstantExpr::getICmp(pred, C2, C1);
 
       case ICmpInst::ICMP_ULT:
       case ICmpInst::ICMP_SLT:
@@ -1858,7 +1860,7 @@ Constant *llvm::ConstantFoldCompareInstruction(LLVMContext &Context,
       case ICmpInst::ICMP_SGE:
         // Change the predicate as necessary to swap the operands.
         pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred);
-        return ConstantFoldCompareInstruction(Context, pred, C2, C1);
+        return ConstantExpr::getICmp(pred, C2, C1);
 
       default:  // These predicates cannot be flopped around.
         break;

diff --git a/test/Transforms/InstCombine/constant-fold-compare.ll b/test/Transforms/InstCombine/constant-fold-compare.ll
new file mode 100644 (file)
index 0000000..6e41e2f
--- /dev/null
+++ b/test/Transforms/InstCombine/constant-fold-compare.ll
@@ -0,0 +1,8 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
+
+define i32 @a() nounwind readnone {
+entry:
+  ret i32 zext (i1 icmp eq (i32 0, i32 ptrtoint (i32 ()* @a to i32)) to i32)
+}
+; CHECK: ret i32 0