From 0d1969024c6fd7fa9aa729cf17860d0c172b56e0 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Mon, 12 Aug 2019 01:53:46 -0700
Subject: Revert "expr: Fix cast of same type"

This reverts commit 1a38a5fc4844a0de8729be694a62ba0afce3ff52.

This breaks comparisons bitfields in some cases, for instance

	extern struct {unsigned x:31;} s;
	int main(void) {
		return (unsigned)s.x - 1 < 0;
	}

If we discard the cast, then it is a signed comparison because of integer
promotion for bit-fields, otherwise it is an unsigned comparison.

Additionally, the test case this was meant to fix is not actually ISO C,
since casts must be to scalar types or `void`.
---
 expr.c                  | 40 +++++++++++++++++++---------------------
 test/cast-same-type.qbe | 12 ------------
 2 files changed, 19 insertions(+), 33 deletions(-)
 delete mode 100644 test/cast-same-type.qbe

diff --git a/expr.c b/expr.c
index 2879efe..171c239 100644
--- a/expr.c
+++ b/expr.c
@@ -866,40 +866,38 @@ unaryexpr(struct scope *s)
 static struct expr *
 castexpr(struct scope *s)
 {
-	struct type *t, *prev = NULL;
+	struct type *t;
 	enum typequal tq;
-	struct expr *result, *base = NULL, **end = &result;
+	struct expr *r, *e, **end;
 
+	end = &r;
 	while (consume(TLPAREN)) {
 		tq = QUALNONE;
 		t = typename(s, &tq);
 		if (!t) {
-			base = expr(s);
+			e = expr(s);
 			expect(TRPAREN, "after expression to match '('");
-			base = postfixexpr(s, base);
-			break;
+			*end = postfixexpr(s, e);
+			return r;
 		}
 		expect(TRPAREN, "after type name");
 		if (tok.kind == TLBRACE) {
-			base = mkexpr(EXPRCOMPOUND, t);
-			base->qual = tq;
-			base->lvalue = true;
-			base->compound.init = parseinit(s, t);
-			base = postfixexpr(s, decay(base));
-			break;
-		}
-		if (prev && !typecompatible(prev, t)) {
-			*end = mkexpr(EXPRCAST, prev);
-			// XXX check types 6.5.4
-			end = &(*end)->base;
+			e = mkexpr(EXPRCOMPOUND, t);
+			e->qual = tq;
+			e->lvalue = true;
+			e->compound.init = parseinit(s, t);
+			e = decay(e);
+			*end = postfixexpr(s, e);
+			return r;
 		}
-		prev = t;
+		e = mkexpr(EXPRCAST, t);
+		// XXX check types 6.5.4
+		*end = e;
+		end = &e->base;
 	}
-	if (!base)
-		base = unaryexpr(s);
-	*end = prev ? exprconvert(base, prev) : base;
+	*end = unaryexpr(s);
 
-	return result;
+	return r;
 }
 
 static int
diff --git a/test/cast-same-type.qbe b/test/cast-same-type.qbe
deleted file mode 100644
index 625f937..0000000
--- a/test/cast-same-type.qbe
+++ /dev/null
@@ -1,12 +0,0 @@
-export
-function w $main() {
-@start.1
-@body.2
-	%.1 =l copy $s
-	%.2 =l mul 0, 1
-	%.3 =l add %.1, %.2
-	%.4 =l copy %.3
-	%.5 =w loadsw %.4
-	ret %.5
-}
-export data $s = align 4 { z 4 }
-- 
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