[RISC-V][PR target/116256] Fix incorrect return value for predicate

Another bug found while chasing paths to fix the remaining issues in pr116256.

This case is sometimes benign when the optimizers are enabled.  But could show
up in a -O0 compile with some patterns I was playing around with.

Basically we have a predicate that is meant to return true if bits set in the
operand are all consecutive.

That predicate would return the wrong value when presented with (const_int 0)
indicating it had a run of on bits when obviously no bits are on 😉

It's pretty obvious once you look at the implementation.

if (exact_log2 ((val >> ctz_hwi (val)) + 1) < 0)
  return false
return true;

The right shift is always going to produce 0.  0 + 1 = 1 which is a power of 2.
So exact_log2 returns 0 and we get a true result rather than a false result.

The fix is trivial.  "<=".  While inside we might as well fix the formatting.

Tested on rv32 and rv64 in my tester.  Waiting on upstream pre-commit testing
to render a verdict.

	PR target/116256
gcc/
	* config/riscv/predicates.md (consecutive_bits_operand): Properly
	handle (const_int 0).

diff --git a/gcc/config/riscv/predicates.md b/gcc/config/riscv/predicates.md
index 1f67d30be9d95566b8c181bdf140dbf8648d4f5b..f26bafcc688be66a364b728f5cf5762b976afdd4 100644 (file)
--- a/gcc/config/riscv/predicates.md
+++ b/gcc/config/riscv/predicates.md
@@ -423,11 +423,11 @@
 (define_predicate "consecutive_bits_operand"
   (match_code "const_int")
 {
-       unsigned HOST_WIDE_INT val = UINTVAL (op);
-       if (exact_log2 ((val >> ctz_hwi (val)) + 1) < 0)
-               return false;
+  unsigned HOST_WIDE_INT val = UINTVAL (op);
+  if (exact_log2 ((val >> ctz_hwi (val)) + 1) <= 0)
+    return false;
 
-       return true;
+  return true;
 })
 
 (define_predicate "const_two_s12"