From: Richard Earnshaw <rearnsha@arm.com>
Date: Wed, 4 Feb 2026 14:14:37 +0000 (+0000)
Subject: compare-elim: arm: enable compare-elimination on Arm [PR123604]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c4d53bc3c96770438d63a0d35a638beabad67c65;p=thirdparty%2Fgcc.git

compare-elim: arm: enable compare-elimination on Arm [PR123604]

The Arm port has never had the compare elimination pass enabled by
adding a definition of TARGET_FLAGS_REGNUM.  But just adding this is
insufficient because the target uses COND_EXEC and compare-elim is not
yet set up to handle this.

This seems to be quite simple, since we just need to recognize
COND_EXEC in insns when scanning for uses of the condition code
register.

This is a partial mitigation for the code quality regression
reported in PR target/123604.

gcc/ChangeLog:

	PR target/123604
	* compare-elim.cc (find_flags_uses_in_insn): Handle COND_EXEC.
	* config/arm/arm.cc (TARGET_FLAGS_REGNUM): Define.
---

diff --git a/gcc/compare-elim.cc b/gcc/compare-elim.cc
index 006d4e35efc..723f9e31c79 100644
--- a/gcc/compare-elim.cc
+++ b/gcc/compare-elim.cc
@@ -258,6 +258,8 @@ find_flags_uses_in_insn (struct comparison *cmp, rtx_insn *insn)
 	  x = SET_SRC (x);
 	if (GET_CODE (x) == IF_THEN_ELSE)
 	  x = XEXP (x, 0);
+	if (GET_CODE (x) == COND_EXEC)
+	  x = COND_EXEC_TEST (x);
 	if (COMPARISON_P (x)
 	    && loc == &XEXP (x, 0)
 	    && XEXP (x, 1) == const0_rtx)
diff --git a/gcc/config/arm/arm.cc b/gcc/config/arm/arm.cc
index 0a1f6612d07..ff3400ae035 100644
--- a/gcc/config/arm/arm.cc
+++ b/gcc/config/arm/arm.cc
@@ -839,6 +839,9 @@ static const scoped_attribute_specs *const arm_attribute_table[] =
 
 #undef TARGET_VECTORIZE_GET_MASK_MODE
 #define TARGET_VECTORIZE_GET_MASK_MODE arm_get_mask_mode
+
+#undef TARGET_FLAGS_REGNUM
+#define TARGET_FLAGS_REGNUM CC_REGNUM
 
 /* Obstack for minipool constant handling.  */
 static struct obstack minipool_obstack;