x86-always-generate-branch-hint.patch

From ecb8284b8bec4f9e025d21177efbe13f64f6f11b Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 26 Apr 2022 11:08:55 -0700
Subject: [PATCH] x86: Always generate branch hint

For -mtune-ctrl=branch_prediction_hints, always generate branch hint for
conditional branches.

gcc/

	* config/i386/i386.cc (ix86_print_operand): Always generate
	branch hint for conditional branches.

gcc/testsuite/

	* gcc.target/i386/branch-hint-1.c: New test.
---
 gcc/config/i386/i386.cc                       | 26 +++++--------------
 gcc/testsuite/gcc.target/i386/branch-hint-1.c | 16 ++++++++++++
 2 files changed, 23 insertions(+), 19 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/branch-hint-1.c

diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 52040da8c47f..8246576f7b82 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -13555,25 +13555,13 @@ ix86_print_operand (FILE *file, rtx x, int code)
 		int pred_val = profile_probability::from_reg_br_prob_note
 				 (XINT (x, 0)).to_reg_br_prob_base ();
 
-		if (pred_val < REG_BR_PROB_BASE * 45 / 100
-		    || pred_val > REG_BR_PROB_BASE * 55 / 100)
-		  {
-		    bool taken = pred_val > REG_BR_PROB_BASE / 2;
-		    bool cputaken
-		      = final_forward_branch_p (current_output_insn) == 0;
-
-		    /* Emit hints only in the case default branch prediction
-		       heuristics would fail.  */
-		    if (taken != cputaken)
-		      {
-			/* We use 3e (DS) prefix for taken branches and
-			   2e (CS) prefix for not taken branches.  */
-			if (taken)
-			  fputs ("ds ; ", file);
-			else
-			  fputs ("cs ; ", file);
-		      }
-		  }
+		bool taken = pred_val > REG_BR_PROB_BASE / 2;
+		/* We use 3e (DS) prefix for taken branches and
+		   2e (CS) prefix for not taken branches.  */
+		if (taken)
+		  fputs ("ds ; ", file);
+		else
+		  fputs ("cs ; ", file);
 	      }
 	    return;
 	  }
diff --git a/gcc/testsuite/gcc.target/i386/branch-hint-1.c b/gcc/testsuite/gcc.target/i386/branch-hint-1.c
new file mode 100644
index 000000000000..03dd83b05af0
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/branch-hint-1.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -dp -mtune-ctrl=branch_prediction_hints" } */
+
+int
+main (int argc, char** argv)
+{
+  if (argc == 1)
+    return 1;
+
+  if (argc == 2)
+    return 2;
+
+  return 3;
+}
+
+/* { dg-final { scan-assembler-not "\tj\[a-z\]\+\[ \\t\]+.* \\*jcc" } } */