If-conversion RFC 4 - x86 only (for now), use cmovXX

Replacement of tiny conditional jump graphlets with
conditional move instructions.

Currently enabled only for x86. Arm64 support using cselXX
will be essentially identical.

Adds (internal) frontend sel0/sel1 ops with flag-specific
backend xselXX following jnz implementation pattern.

Testing: standard QBE, cproc, harec, hare, roland

1 files changed, 8 insertions, 0 deletions

diff --git a/main.c b/main.c
index 7a97f8a..f7180ce 100644
--- a/main.c
+++ b/main.c
@@ -11,6 +11,7 @@ char debug['Z'+1] = {
 	['N'] = 0, /* ssa construction */
 	['C'] = 0, /* copy elimination */
 	['F'] = 0, /* constant folding */
+	['K'] = 0, /* if-conversion */
 	['A'] = 0, /* abi lowering */
 	['I'] = 0, /* instruction selection */
 	['L'] = 0, /* liveness */
@@ -81,6 +82,13 @@ func(Fn *fn)
 	gcm(fn);
 	filluse(fn);
 	ssacheck(fn);
+	if (T.cansel) {
+		ifconvert(fn);
+		fillcfg(fn);
+		filluse(fn);
+		filldom(fn);
+		ssacheck(fn);
+	}
 	T.abi1(fn);
 	simpl(fn);
 	fillcfg(fn);