See also PR4973
//===---------------------------------------------------------------------===//
-
-I saw this constant expression in real code after llvm-g++ -O2:
-
-declare extern_weak i32 @0(i64)
-
-define void @foo() {
- br i1 icmp eq (i32 zext (i1 icmp ne (i32 (i64)* @0, i32 (i64)* null) to i32),
-i32 0), label %cond_true, label %cond_false
-cond_true:
- ret void
-cond_false:
- ret void
-}
-
-That branch expression should be reduced to:
-
- i1 icmp eq (i32 (i64)* @0, i32 (i64)* null)
-
-It's probably not a perf issue, I just happened to see it while examining
-something else and didn't want to forget about it.
-
-//===---------------------------------------------------------------------===//
}
}
+ // If the left hand side is an extension, try eliminating it.
+ if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
+ if (CE1->getOpcode() == Instruction::SExt ||
+ CE1->getOpcode() == Instruction::ZExt) {
+ Constant *CE1Op0 = CE1->getOperand(0);
+ Constant *CE1Inverse = ConstantExpr::getTrunc(CE1, CE1Op0->getType());
+ if (CE1Inverse == CE1Op0) {
+ // Check whether we can safely truncate the right hand side.
+ Constant *C2Inverse = ConstantExpr::getTrunc(C2, CE1Op0->getType());
+ if (ConstantExpr::getZExt(C2Inverse, C2->getType()) == C2) {
+ return ConstantExpr::getICmp(pred, CE1Inverse, C2Inverse);
+ }
+ }
+ }
+ }
+
if (!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) {
// If C2 is a constant expr and C1 isn't, flip them around and fold the
// other way if possible.
; CHECK: @M = global i1 icmp uge (i8* @X, i8* @Y) ; <i1*> [#uses=0]
@N = global i1 icmp ne (i1 icmp ult (i8* @X, i8* @Y), i1 false)
; CHECK: @N = global i1 icmp ult (i8* @X, i8* @Y) ; <i1*> [#uses=0]
+
+@O = global i1 icmp eq (i32 zext (i1 icmp ult (i8* @X, i8* @Y) to i32), i32 0)
+; CHECK: @O = global i1 icmp uge (i8* @X, i8* @Y) ; <i1*> [#uses=0]