interp: add support for constant icmp instructions

These instructions sometimes pop up in LLVM 15, but they never occured
in LLVM 14. Implementing them is relatively straightforward: simply
generalize the code that already exists for llvm.ICmp interpreting.

interp/interpreter.go

@@ -723,46 +723,9 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 			locals[inst.localIndex] = newagg
 		case llvm.ICmp:
 			predicate := llvm.IntPredicate(operands[2].(literalValue).value.(uint8))
-			var result bool
 			lhs := operands[0]
 			rhs := operands[1]
-			switch predicate {
-			case llvm.IntEQ, llvm.IntNE:
-				lhsPointer, lhsErr := lhs.asPointer(r)
-				rhsPointer, rhsErr := rhs.asPointer(r)
-				if (lhsErr == nil) != (rhsErr == nil) {
-					// Fast path: only one is a pointer, so they can't be equal.
-					result = false
-				} else if lhsErr == nil {
-					// Both must be nil, so both are pointers.
-					// Compare them directly.
-					result = lhsPointer.equal(rhsPointer)
-				} else {
-					// Fall back to generic comparison.
-					result = lhs.asRawValue(r).equal(rhs.asRawValue(r))
-				}
-				if predicate == llvm.IntNE {
-					result = !result
-				}
-			case llvm.IntUGT:
-				result = lhs.Uint() > rhs.Uint()
-			case llvm.IntUGE:
-				result = lhs.Uint() >= rhs.Uint()
-			case llvm.IntULT:
-				result = lhs.Uint() < rhs.Uint()
-			case llvm.IntULE:
-				result = lhs.Uint() <= rhs.Uint()
-			case llvm.IntSGT:
-				result = lhs.Int() > rhs.Int()
-			case llvm.IntSGE:
-				result = lhs.Int() >= rhs.Int()
-			case llvm.IntSLT:
-				result = lhs.Int() < rhs.Int()
-			case llvm.IntSLE:
-				result = lhs.Int() <= rhs.Int()
-			default:
-				return nil, mem, r.errorAt(inst, errors.New("interp: unsupported icmp"))
-			}
+			result := r.interpretICmp(lhs, rhs, predicate)
 			if result {
 				locals[inst.localIndex] = literalValue{uint8(1)}
 			} else {
@@ -948,6 +911,51 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 	return nil, mem, r.errorAt(bb.instructions[len(bb.instructions)-1], errors.New("interp: reached end of basic block without terminator"))
 }
 
+// Interpret an icmp instruction. Doesn't have side effects, only returns the
+// output of the comparison.
+func (r *runner) interpretICmp(lhs, rhs value, predicate llvm.IntPredicate) bool {
+	switch predicate {
+	case llvm.IntEQ, llvm.IntNE:
+		var result bool
+		lhsPointer, lhsErr := lhs.asPointer(r)
+		rhsPointer, rhsErr := rhs.asPointer(r)
+		if (lhsErr == nil) != (rhsErr == nil) {
+			// Fast path: only one is a pointer, so they can't be equal.
+			result = false
+		} else if lhsErr == nil {
+			// Both must be nil, so both are pointers.
+			// Compare them directly.
+			result = lhsPointer.equal(rhsPointer)
+		} else {
+			// Fall back to generic comparison.
+			result = lhs.asRawValue(r).equal(rhs.asRawValue(r))
+		}
+		if predicate == llvm.IntNE {
+			result = !result
+		}
+		return result
+	case llvm.IntUGT:
+		return lhs.Uint() > rhs.Uint()
+	case llvm.IntUGE:
+		return lhs.Uint() >= rhs.Uint()
+	case llvm.IntULT:
+		return lhs.Uint() < rhs.Uint()
+	case llvm.IntULE:
+		return lhs.Uint() <= rhs.Uint()
+	case llvm.IntSGT:
+		return lhs.Int() > rhs.Int()
+	case llvm.IntSGE:
+		return lhs.Int() >= rhs.Int()
+	case llvm.IntSLT:
+		return lhs.Int() < rhs.Int()
+	case llvm.IntSLE:
+		return lhs.Int() <= rhs.Int()
+	default:
+		// _should_ be unreachable, until LLVM adds new icmp operands (unlikely)
+		panic("interp: unsupported icmp")
+	}
+}
+
 func (r *runner) runAtRuntime(fn *function, inst instruction, locals []value, mem *memoryView, indent string) *Error {
 	numOperands := inst.llvmInst.OperandsCount()
 	operands := make([]llvm.Value, numOperands)

interp/memory.go

@@ -1031,6 +1031,17 @@ func (v *rawValue) set(llvmValue llvm.Value, r *runner) {
 			for i := uint32(0); i < ptrSize; i++ {
 				v.buf[i] = ptrValue.pointer
 			}
+		case llvm.ICmp:
+			size := r.targetData.TypeAllocSize(llvmValue.Operand(0).Type())
+			lhs := newRawValue(uint32(size))
+			rhs := newRawValue(uint32(size))
+			lhs.set(llvmValue.Operand(0), r)
+			rhs.set(llvmValue.Operand(1), r)
+			if r.interpretICmp(lhs, rhs, llvmValue.IntPredicate()) {
+				v.buf[0] = 1 // result is true
+			} else {
+				v.buf[0] = 0 // result is false
+			}
 		default:
 			llvmValue.Dump()
 			println()

interp/testdata/consteval.ll

@@ -3,6 +3,7 @@ target triple = "x86_64--linux"
 
 @intToPtrResult = global i8 0
 @ptrToIntResult = global i8 0
+@icmpResult = global i8 0
 @someArray = internal global {i16, i8, i8} zeroinitializer
 @someArrayPointer = global i8* zeroinitializer
 
@@ -15,6 +16,7 @@ define internal void @main.init() {
   call void @testIntToPtr()
   call void @testPtrToInt()
   call void @testConstGEP()
+  call void @testICmp()
   ret void
 }
 
@@ -48,3 +50,16 @@ define internal void @testConstGEP() {
   store i8* getelementptr inbounds (i8, i8* bitcast ({i16, i8, i8}* @someArray to i8*), i32 2), i8** @someArrayPointer
   ret void
 }
+
+define internal void @testICmp() {
+  br i1 icmp eq (i64 ptrtoint (i8* @ptrToIntResult to i64), i64 0), label %equal, label %unequal
+equal:
+  ; should not be reached
+  store i8 1, i8* @icmpResult
+  ret void
+unequal:
+  ; should be reached
+  store i8 2, i8* @icmpResult
+  ret void
+  ret void
+}

interp/testdata/consteval.out.ll

@@ -3,6 +3,7 @@ target triple = "x86_64--linux"
 
 @intToPtrResult = local_unnamed_addr global i8 2
 @ptrToIntResult = local_unnamed_addr global i8 2
+@icmpResult = local_unnamed_addr global i8 2
 @someArray = internal global { i16, i8, i8 } zeroinitializer
 @someArrayPointer = local_unnamed_addr global i8* getelementptr inbounds ({ i16, i8, i8 }, { i16, i8, i8 }* @someArray, i64 0, i32 1)