Add test case for #203

left_shift() adapts the example from @davidgiven that caused `ack -O3`
to crash.  multiply() is a similar example.

Edit the build system to use -O3 for this test.  It now takes -O3 from
the test's filename, and still defaults to -O0.

tests/plat/bugs/bug-203-ego-sr_c-O3.c

@@ -0,0 +1,47 @@
+#include "test.h"
+
+/*
+ * https://github.com/davidgiven/ack/issues/203 was a bug in the
+ * strength reduction (SR) phase of ego.  To cause the bug:
+ *
+ *  1. SR must run; it runs at `ack -O3` and higher.
+ *
+ *  2. SR must find a loop with an induction variable, and SR must
+ *     find at least 2 different expressions using the variable, like
+ *     i << 1, (i + 1) << 1, or 3 * i, 5 * i.
+ *
+ *  3. There is no basic block to act as a loop header, so SR must
+ *     create the block.  One way is to put if (one) { ... } around
+ *     the loop, so the loop is just after a conditional branch.
+ */
+
+/*
+ * Global variables prevent optimizations:
+ * if (one) { ... } caused the bug, if (1) { ... } didn't.
+ */
+int zero = 0;
+int one = 1;
+short ary[] = {8, 8, 8, 8, 8, 9};
+
+int left_shift(int i) {
+	if (one) {
+		/* EM will use i << 1, (i + 1) << 1 here. */
+		while (ary[i] == ary[i + 1])
+			i++;
+	}
+	return i;
+}
+
+int multiply(int i) {
+	if (one) {
+		while (((3 * i) & (5 * i)) < 40)
+			i++;
+	}
+	return i;
+}
+
+int main(void) {
+	ASSERT(left_shift(zero) == 4);
+	ASSERT(multiply(zero) == 21);
+	finished();
+}

tests/plat/build.lua

@@ -5,7 +5,7 @@ definerule("plat_testsuite",
 	{
 		plat = { type="string" },
 		method = { type="string" },
-		-- added long-long/llswitch_e.c
+		-- added bugs/bug-203-ego-sr_c-O3.c
 		sets = { type="table", default={"core", "b", "bugs", "m2", "floats", "long-long"}},
 		skipsets = { type="table", default={}},
 		tests = { type="targets", default={} },
@@ -48,6 +48,14 @@ definerule("plat_testsuite",
 				lang = "e"
 			end
 
+			-- If lang is "c-O3", then build with -O3.
+			local _, _, optimize = lang:find("(-O[^-]*)$")
+			if optimize then
+				lang = lang:sub(1, -1 - #optimize)
+			else
+				optimize = "-O0"
+			end
+
 			local bin = ackprogram {
 				name = fs.."_bin",
 				srcs = { f },
@@ -55,7 +63,7 @@ definerule("plat_testsuite",
 				vars = {
 					plat = e.plat,
 					lang = lang,
-					ackcflags = "-O0 -Bmain"
+					ackcflags = optimize.." -Bmain"
 				}
 			}