From: Alexandre Oliva <oliva@adacore.com>
Date: Wed, 10 Dec 2025 23:56:17 +0000 (-0300)
Subject: x86: improve lea peepholes
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0ff1ea6a6a2ec7dc57c962920e790d94cd286f39;p=thirdparty%2Fgcc.git

x86: improve lea peepholes

gcc.target/i386/lea-3.c fails on ia32 with PIE enabled by default.
There are two reasons for that:

- setting up the PIC register requires one addl instruction, and the
  testcase wants none

- the expected lea-combining peephole doesn't get applied for two
  reasons:

-- the second insn of the pair that could be turned into a single lea
   doesn't clobber CC, but the existing peephole2 requires an add with
   such a clobber

-- the first and second insns set different regs, and the existing
   peephole2 requires them to be the same

Add extra peephole2s for when the second insn doesn't clobber CC, and
for when the first set reg is different, but it dies at the second
insn.

Adjust lea-3.c to run with -fno-PIE, and add lea-4.c with -fPIE.

The last of the newly-added peephole2s, that enables lea-4.c to pass,
also hits during an i686-linux-gnu bootstrap (without PIE enabled),
while building shared libraries for the target.  I haven't been able
to exercise the other 2, but I haven't tried very hard, and I see no
why they couldn't possibly hit, so I left them in.


for  gcc/ChangeLog

	* config/i386/i386.md (lea peephole2): Add 3 new variants.

for  gcc/testsuite/ChangeLog

	* gcc.target/i386/lea-3.c: Add -fno-PIE.
	* gcc.target/i386/lea-4.c: New, with -fPIE.
---

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index df7135f84d4..b5d83893425 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -6452,6 +6452,48 @@
   [(set (match_dup 0) (plus:SWI48 (plus:SWI48 (match_dup 0)
 					      (match_dup 1))
 				  (match_dup 2)))])
+
+(define_peephole2
+  [(parallel [(set (match_operand:SWI48 0 "register_operand")
+		   (plus:SWI48 (match_dup 0)
+			       (match_operand 1 "register_operand")))
+	      (clobber (reg:CC FLAGS_REG))])
+   (set (match_dup 0)
+	(plus:SWI48 (match_dup 0)
+		    (match_operand 2 "x86_64_immediate_operand")))]
+  "!TARGET_AVOID_LEA_FOR_ADDR || optimize_function_for_size_p (cfun)"
+  [(set (match_dup 0) (plus:SWI48 (plus:SWI48 (match_dup 0)
+					      (match_dup 1))
+				  (match_dup 2)))])
+
+(define_peephole2
+  [(parallel [(set (match_operand:SWI48 0 "register_operand")
+		   (plus:SWI48 (match_dup 0)
+			       (match_operand 1 "register_operand")))
+	      (clobber (reg:CC FLAGS_REG))])
+   (parallel [(set (match_operand:SWI48 3 "register_operand")
+		   (plus:SWI48 (match_dup 0)
+			       (match_operand 2 "x86_64_immediate_operand")))
+	      (clobber (reg:CC FLAGS_REG))])]
+  "(!TARGET_AVOID_LEA_FOR_ADDR || optimize_function_for_size_p (cfun))
+   && peep2_reg_dead_p (2, operands[0])"
+  [(set (match_dup 3) (plus:SWI48 (plus:SWI48 (match_dup 0)
+					      (match_dup 1))
+				  (match_dup 2)))])
+
+(define_peephole2
+  [(parallel [(set (match_operand:SWI48 0 "register_operand")
+		   (plus:SWI48 (match_dup 0)
+			       (match_operand 1 "register_operand")))
+	      (clobber (reg:CC FLAGS_REG))])
+   (set (match_operand:SWI48 3 "register_operand")
+	(plus:SWI48 (match_dup 0)
+		    (match_operand 2 "x86_64_immediate_operand")))]
+  "(!TARGET_AVOID_LEA_FOR_ADDR || optimize_function_for_size_p (cfun))
+   && peep2_reg_dead_p (2, operands[0])"
+  [(set (match_dup 3) (plus:SWI48 (plus:SWI48 (match_dup 0)
+					      (match_dup 1))
+				  (match_dup 2)))])
 
 ;; Add instructions
 
diff --git a/gcc/testsuite/gcc.target/i386/lea-3.c b/gcc/testsuite/gcc.target/i386/lea-3.c
index 84e66b00fc2..ce50531f935 100644
--- a/gcc/testsuite/gcc.target/i386/lea-3.c
+++ b/gcc/testsuite/gcc.target/i386/lea-3.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2" } */
+/* { dg-options "-O2 -fno-PIE" } */
 
 int m;
 
diff --git a/gcc/testsuite/gcc.target/i386/lea-4.c b/gcc/testsuite/gcc.target/i386/lea-4.c
new file mode 100644
index 00000000000..7bb2cec6d85
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/lea-4.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fPIE" } */
+/* Same as lea-3.c, but with -fPIE.  On ia32, that requires setting up the PIC
+   register, which requires an addl instruction.  */
+
+int m;
+
+int foo(int y)
+{
+  return (m+y-1)/y;
+}
+
+/* { dg-final { scan-assembler "leal" } } */
+/* { dg-final { scan-assembler-not "addl" { target lp64 } } } */
+/* { dg-final { scan-assembler-times "addl" 1 { target ia32 } } } */
+/* { dg-final { scan-assembler-not "subl" } } */