Merge pull request #1632 from gitlost/const_in_if_#1592

Fix issue #1592 "LLVM code gen error when using a constant in an if"

3 files changed, 18 insertions, 6 deletions

diff --git a/src/llvm_backend_expr.cpp b/src/llvm_backend_expr.cpp
index 4294747b9..133df4d41 100644
--- a/src/llvm_backend_expr.cpp
+++ b/src/llvm_backend_expr.cpp
@@ -3028,7 +3028,7 @@ lbValue lb_build_expr(lbProcedure *p, Ast *expr) {
 		lbBlock *done  = lb_create_block(p, "if.done"); // NOTE(bill): Append later
 		lbBlock *else_ = lb_create_block(p, "if.else");
 
-		lbValue cond = lb_build_cond(p, te->cond, then, else_);
+		lb_build_cond(p, te->cond, then, else_);
 		lb_start_block(p, then);
 
 		Type *type = default_type(type_of_expr(expr));
@@ -4646,7 +4646,7 @@ lbAddr lb_build_addr(lbProcedure *p, Ast *expr) {
 		lbBlock *done  = lb_create_block(p, "if.done"); // NOTE(bill): Append later
 		lbBlock *else_ = lb_create_block(p, "if.else");
 
-		lbValue cond = lb_build_cond(p, te->cond, then, else_);
+		lb_build_cond(p, te->cond, then, else_);
 		lb_start_block(p, then);
 
 		Type *ptr_type = alloc_type_pointer(default_type(type_of_expr(expr)));
diff --git a/src/llvm_backend_general.cpp b/src/llvm_backend_general.cpp
index 1c98aa77f..dd1555193 100644
--- a/src/llvm_backend_general.cpp
+++ b/src/llvm_backend_general.cpp
@@ -2602,6 +2602,9 @@ lbValue lb_build_cond(lbProcedure *p, Ast *cond, lbBlock *true_block, lbBlock *f
 	GB_ASSERT(true_block  != nullptr);
 	GB_ASSERT(false_block != nullptr);
 
+	// Use to signal not to do compile time short circuit for consts
+	lbValue no_comptime_short_circuit = {};
+
 	switch (cond->kind) {
 	case_ast_node(pe, ParenExpr, cond);
 		return lb_build_cond(p, pe->expr, true_block, false_block);
@@ -2609,7 +2612,11 @@ lbValue lb_build_cond(lbProcedure *p, Ast *cond, lbBlock *true_block, lbBlock *f
 
 	case_ast_node(ue, UnaryExpr, cond);
 		if (ue->op.kind == Token_Not) {
-			return lb_build_cond(p, ue->expr, false_block, true_block);
+			lbValue cond_val = lb_build_cond(p, ue->expr, false_block, true_block);
+			if (cond_val.value && LLVMIsConstant(cond_val.value)) {
+				return lb_const_bool(p->module, cond_val.type, LLVMConstIntGetZExtValue(cond_val.value) == 0);
+			}
+			return no_comptime_short_circuit;
 		}
 	case_end;
 
@@ -2618,12 +2625,14 @@ lbValue lb_build_cond(lbProcedure *p, Ast *cond, lbBlock *true_block, lbBlock *f
 			lbBlock *block = lb_create_block(p, "cmp.and");
 			lb_build_cond(p, be->left, block, false_block);
 			lb_start_block(p, block);
-			return lb_build_cond(p, be->right, true_block, false_block);
+			lb_build_cond(p, be->right, true_block, false_block);
+			return no_comptime_short_circuit;
 		} else if (be->op.kind == Token_CmpOr) {
 			lbBlock *block = lb_create_block(p, "cmp.or");
 			lb_build_cond(p, be->left, true_block, block);
 			lb_start_block(p, block);
-			return lb_build_cond(p, be->right, true_block, false_block);
+			lb_build_cond(p, be->right, true_block, false_block);
+			return no_comptime_short_circuit;
 		}
 	case_end;
 	}
diff --git a/src/llvm_backend_stmt.cpp b/src/llvm_backend_stmt.cpp
index 916c0433e..2afb5300b 100644
--- a/src/llvm_backend_stmt.cpp
+++ b/src/llvm_backend_stmt.cpp
@@ -1652,13 +1652,16 @@ void lb_build_if_stmt(lbProcedure *p, Ast *node) {
 	}
 
 	lbValue cond = lb_build_cond(p, is->cond, then, else_);
+	// Note `cond.value` only set for non-and/or conditions and const negs so that the `LLVMIsConstant()`
+	// and `LLVMConstIntGetZExtValue()` calls below will be valid and `LLVMInstructionEraseFromParent()`
+	// will target the correct (& only) branch statement
 
 	if (is->label != nullptr) {
 		lbTargetList *tl = lb_push_target_list(p, is->label, done, nullptr, nullptr);
 		tl->is_block = true;
 	}
 
-	if (LLVMIsConstant(cond.value)) {
+	if (cond.value && LLVMIsConstant(cond.value)) {
 		// NOTE(bill): Do a compile time short circuit for when the condition is constantly known.
 		// This done manually rather than relying on the SSA passes because sometimes the SSA passes
 		// miss some even if they are constantly known, especially with few optimization passes.