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* [gcc r12-7616] PR tree-optimization/98335: New peephole2 xorl; movb -> movzbl
@ 2022-03-11 17:59 Roger Sayle
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From: Roger Sayle @ 2022-03-11 17:59 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:251ea6dfbdb4448875e41081682bb3aa451b5729
commit r12-7616-g251ea6dfbdb4448875e41081682bb3aa451b5729
Author: Roger Sayle <roger@nextmovesoftware.com>
Date: Fri Mar 11 17:57:12 2022 +0000
PR tree-optimization/98335: New peephole2 xorl;movb -> movzbl
This patch is the backend piece of my proposed fix to PR tree-opt/98335,
to allow C++ partial struct initialization to be as efficient/optimized
as full struct initialization.
With the middle-end patch just posted to gcc-patches, the test case
in the PR compiles on x86_64-pc-linux-gnu with -O2 to:
xorl %eax, %eax
movb c(%rip), %al
ret
with this additional peephole2 (actually four peephole2s):
movzbl c(%rip), %eax
ret
2022-03-11 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
PR tree-optimization/98335
* config/i386/i386.md (peephole2): Eliminate redundant insv.
Combine movl followed by movb. Transform xorl followed by
a suitable movb or movw into the equivalent movz[bw]l.
gcc/testsuite/ChangeLog
PR tree-optimization/98335
* g++.target/i386/pr98335.C: New test case.
* gcc.target/i386/pr98335.c: New test case.
Diff:
---
gcc/config/i386/i386.md | 50 +++++++++++++++++++++++++++++++++
gcc/testsuite/g++.target/i386/pr98335.C | 18 ++++++++++++
gcc/testsuite/gcc.target/i386/pr98335.c | 12 ++++++++
3 files changed, 80 insertions(+)
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index d15170e8acf..c8fbf605e41 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -3180,6 +3180,38 @@
(const_int 8))
(subreg:SWI248 (match_dup 1) 0))])
+;; Eliminate redundant insv, e.g. xorl %eax,%eax; movb $0, %ah
+(define_peephole2
+ [(parallel [(set (match_operand:SWI48 0 "general_reg_operand")
+ (const_int 0))
+ (clobber (reg:CC FLAGS_REG))])
+ (set (zero_extract:SWI248 (match_operand:SWI248 1 "general_reg_operand")
+ (const_int 8)
+ (const_int 8))
+ (const_int 0))]
+ "REGNO (operands[0]) == REGNO (operands[1])"
+ [(parallel [(set (match_operand:SWI48 0 "general_reg_operand")
+ (const_int 0))
+ (clobber (reg:CC FLAGS_REG))])])
+
+;; Combine movl followed by movb.
+(define_peephole2
+ [(set (match_operand:SWI48 0 "general_reg_operand")
+ (match_operand:SWI48 1 "const_int_operand"))
+ (set (zero_extract:SWI248 (match_operand:SWI248 2 "general_reg_operand")
+ (const_int 8)
+ (const_int 8))
+ (match_operand:SWI248 3 "const_int_operand"))]
+ "REGNO (operands[0]) == REGNO (operands[2])"
+ [(set (match_operand:SWI48 0 "general_reg_operand")
+ (match_dup 4))]
+{
+ HOST_WIDE_INT tmp = INTVAL (operands[1]) & ~(HOST_WIDE_INT)0xff00;
+ tmp |= (INTVAL (operands[3]) & 0xff) << 8;
+ operands[4] = gen_int_mode (tmp, <SWI48:MODE>mode);
+})
+
+
(define_code_iterator any_extract [sign_extract zero_extract])
(define_insn "*insvqi_2"
@@ -4276,6 +4308,24 @@
[(set_attr "isa" "*,avx512dq,avx512dq")
(set_attr "type" "imovx,mskmov,mskmov")
(set_attr "mode" "SI,QI,QI")])
+
+;; Transform xorl; mov[bw] (set strict_low_part) into movz[bw]l.
+(define_peephole2
+ [(parallel [(set (match_operand:SWI48 0 "general_reg_operand")
+ (const_int 0))
+ (clobber (reg:CC FLAGS_REG))])
+ (set (strict_low_part (match_operand:SWI12 1 "general_reg_operand"))
+ (match_operand:SWI12 2 "nonimmediate_operand"))]
+ "REGNO (operands[0]) == REGNO (operands[1])"
+ [(set (match_dup 0) (zero_extend:SWI48 (match_dup 2)))])
+
+;; Likewise, but preserving FLAGS_REG.
+(define_peephole2
+ [(set (match_operand:SWI48 0 "general_reg_operand") (const_int 0))
+ (set (strict_low_part (match_operand:SWI12 1 "general_reg_operand"))
+ (match_operand:SWI12 2 "nonimmediate_operand"))]
+ "REGNO (operands[0]) == REGNO (operands[1])"
+ [(set (match_dup 0) (zero_extend:SWI48 (match_dup 2)))])
\f
;; Sign extension instructions
diff --git a/gcc/testsuite/g++.target/i386/pr98335.C b/gcc/testsuite/g++.target/i386/pr98335.C
new file mode 100644
index 00000000000..2581b83ab6a
--- /dev/null
+++ b/gcc/testsuite/g++.target/i386/pr98335.C
@@ -0,0 +1,18 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-O2" } */
+
+struct Data {
+ char a;
+ int b;
+};
+
+char c;
+
+Data val(int idx) {
+ return { c }; // { dg-warning "extended initializer" "c++ 98" { target { c++98_only } } }
+}
+
+/* { dg-final { scan-assembler "movzbl" } } */
+/* { dg-final { scan-assembler-not "xorl" } } */
+/* { dg-final { scan-assembler-not "movb" } } */
+
diff --git a/gcc/testsuite/gcc.target/i386/pr98335.c b/gcc/testsuite/gcc.target/i386/pr98335.c
new file mode 100644
index 00000000000..7fa7ad70dce
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr98335.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+union Data { char a; short b; };
+
+char c;
+
+void val(void) {
+ __asm__ __volatile__ ("" : : "r" ((union Data) { c } )); }
+
+/* { dg-final { scan-assembler "movzbl" } } */
+/* { dg-final { scan-assembler-not "xorl" } } */
+/* { dg-final { scan-assembler-not "movb" } } */
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2022-03-11 17:59 [gcc r12-7616] PR tree-optimization/98335: New peephole2 xorl; movb -> movzbl Roger Sayle
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