expr: Skip codegen for unused expression in conditional with constant expression

This compiles `0 ? e1 : e2` as `e2`, and `1 ? e1 : e2` as `e1`
(while still adjusting the type as necessary).

4 files changed, 33 insertions, 10 deletions

diff --git a/test/conditional-compound-literal.c b/test/conditional-compound-literal.c
index 33a5416..40b8ad6 100644
--- a/test/conditional-compound-literal.c
+++ b/test/conditional-compound-literal.c
@@ -1,4 +1,4 @@
 int main(void) {
-	int x = 0, *p = 0 ? 0 : &(int){x};
+	int x = 0, *p = x ? 0 : &(int){x};
 	return *p;
 }
diff --git a/test/conditional-compound-literal.qbe b/test/conditional-compound-literal.qbe
index 739eea4..d2265c6 100644
--- a/test/conditional-compound-literal.qbe
+++ b/test/conditional-compound-literal.qbe
@@ -3,19 +3,20 @@ function w $main() {
 @start.1
 	%.1 =l alloc4 4
 	%.2 =l alloc8 8
-	%.3 =l alloc4 4
+	%.4 =l alloc4 4
 @body.2
 	storew 0, %.1
-	jnz 0, @cond_true.3, @cond_false.4
+	%.3 =w loadw %.1
+	jnz %.3, @cond_true.3, @cond_false.4
 @cond_true.3
 	jmp @cond_join.5
 @cond_false.4
-	%.4 =w loadw %.1
-	storew %.4, %.3
+	%.5 =w loadw %.1
+	storew %.5, %.4
 @cond_join.5
-	%.5 =l phi @cond_true.3 0, @cond_false.4 %.3
-	storel %.5, %.2
-	%.6 =l loadl %.2
-	%.7 =w loadw %.6
-	ret %.7
+	%.6 =l phi @cond_true.3 0, @cond_false.4 %.4
+	storel %.6, %.2
+	%.7 =l loadl %.2
+	%.8 =w loadw %.7
+	ret %.8
 }
diff --git a/test/conditional-constant.c b/test/conditional-constant.c
new file mode 100644
index 0000000..8ebb2a4
--- /dev/null
+++ b/test/conditional-constant.c
@@ -0,0 +1,6 @@
+int main(void) {
+	if ((0 ? 0 : 123) != 123)
+		return 1;
+	if ((1 ? 456 : 0) != 456)
+		return 1;
+}
diff --git a/test/conditional-constant.qbe b/test/conditional-constant.qbe
new file mode 100644
index 0000000..a14e050
--- /dev/null
+++ b/test/conditional-constant.qbe
@@ -0,0 +1,16 @@
+export
+function w $main() {
+@start.1
+@body.2
+	%.1 =w cnew 123, 123
+	jnz %.1, @if_true.3, @if_false.4
+@if_true.3
+	ret 1
+@if_false.4
+	%.2 =w cnew 456, 456
+	jnz %.2, @if_true.5, @if_false.6
+@if_true.5
+	ret 1
+@if_false.6
+	ret 0
+}