interp: support integer icmp of ptrtoint

This kind of code might be generated by the switch implementation of
func values. The func value is represented as a ptrtoint, and before
calling it, it is compared against 0.

interp/frame.go

@@ -194,20 +194,28 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 			lhs := fr.getLocal(inst.Operand(0)).(*LocalValue).Underlying
 			rhs := fr.getLocal(inst.Operand(1)).(*LocalValue).Underlying
 			predicate := inst.IntPredicate()
-			if predicate == llvm.IntEQ && lhs.Type().TypeKind() == llvm.PointerTypeKind {
-				// Unfortunately, the const propagation in the IR builder
-				// doesn't handle pointer compares of inttoptr values. So we
-				// implement it manually here.
-				lhsNil, ok1 := isPointerNil(lhs)
-				rhsNil, ok2 := isPointerNil(rhs)
+			if predicate == llvm.IntEQ {
+				var lhsZero, rhsZero bool
+				var ok1, ok2 bool
+				if lhs.Type().TypeKind() == llvm.PointerTypeKind {
+					// Unfortunately, the const propagation in the IR builder
+					// doesn't handle pointer compares of inttoptr values. So we
+					// implement it manually here.
+					lhsZero, ok1 = isPointerNil(lhs)
+					rhsZero, ok2 = isPointerNil(rhs)
+				}
+				if lhs.Type().TypeKind() == llvm.IntegerTypeKind {
+					lhsZero, ok1 = isZero(lhs)
+					rhsZero, ok2 = isZero(rhs)
+				}
 				if ok1 && ok2 {
-					if lhsNil && rhsNil {
-						// Both are nil, so this icmp is always evaluated to true.
+					if lhsZero && rhsZero {
+						// Both are zero, so this icmp is always evaluated to true.
 						fr.locals[inst] = &LocalValue{fr.Eval, llvm.ConstInt(fr.Mod.Context().Int1Type(), 1, false)}
 						continue
 					}
-					if lhsNil != rhsNil {
-						// Only one of them is nil, so this comparison must return false.
+					if lhsZero != rhsZero {
+						// Only one of them is zero, so this comparison must return false.
 						fr.locals[inst] = &LocalValue{fr.Eval, llvm.ConstInt(fr.Mod.Context().Int1Type(), 0, false)}
 						continue
 					}

interp/testdata/consteval.ll

@@ -2,6 +2,7 @@ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64--linux"
 
 @intToPtrResult = global i8 0
+@ptrToIntResult = global i8 0
 
 define void @runtime.initAll() {
   call void @main.init()
@@ -10,6 +11,7 @@ define void @runtime.initAll() {
 
 define internal void @main.init() {
   call void @testIntToPtr()
+  call void @testPtrToInt()
   ret void
 }
 
@@ -25,3 +27,16 @@ b:
   store i8 2, i8* @intToPtrResult
   ret void
 }
+
+define internal void @testPtrToInt() {
+  %zero = icmp eq i64 ptrtoint (i8* @ptrToIntResult to i64), 0
+  br i1 %zero, label %a, label %b
+a:
+  ; should not be reached
+  store i8 1, i8* @ptrToIntResult
+  ret void
+b:
+  ; should be reached
+  store i8 2, i8* @ptrToIntResult
+  ret void
+}

interp/testdata/consteval.out.ll

@@ -2,6 +2,7 @@ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64--linux"
 
 @intToPtrResult = local_unnamed_addr global i8 2
+@ptrToIntResult = local_unnamed_addr global i8 2
 
 define void @runtime.initAll() local_unnamed_addr {
   ret void

interp/utils.go

@@ -60,9 +60,9 @@ func isPointerNil(v llvm.Value) (result bool, ok bool) {
 		case llvm.IntToPtr:
 			// Whether a constant inttoptr is nil is easy to
 			// determine.
-			operand := v.Operand(0)
-			if operand.IsConstant() {
-				return operand.ZExtValue() == 0, true
+			result, ok = isZero(v.Operand(0))
+			if ok {
+				return
 			}
 		case llvm.BitCast, llvm.GetElementPtr:
 			// These const instructions are just a kind of wrappers for the
@@ -74,6 +74,26 @@ func isPointerNil(v llvm.Value) (result bool, ok bool) {
 		// A constant pointer null is always null, of course.
 		return true, true
 	}
+	if !v.IsAGlobalValue().IsNil() {
+		// A global value is never null.
+		return false, true
+	}
+	return false, false // not valid
+}
+
+// isZero returns whether the value in v is the integer zero, and whether that
+// can be known right now.
+func isZero(v llvm.Value) (result bool, ok bool) {
+	if !v.IsAConstantExpr().IsNil() {
+		switch v.Opcode() {
+		case llvm.PtrToInt:
+			return isPointerNil(v.Operand(0))
+		}
+	}
+	if !v.IsAConstantInt().IsNil() {
+		val := v.ZExtValue()
+		return val == 0, true
+	}
 	return false, false // not valid
 }