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* [gcc/devel/c++-modules] i386: Improve code generation of smin(x, 0) with -m32.
@ 2020-08-27 18:05 Nathan Sidwell
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From: Nathan Sidwell @ 2020-08-27 18:05 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:e4ced0b60ccb4c944970304cf74f1ee9086e5553
commit e4ced0b60ccb4c944970304cf74f1ee9086e5553
Author: Roger Sayle <roger@nextmovesoftware.com>
Date: Mon Aug 10 21:09:16 2020 +0100
i386: Improve code generation of smin(x,0) with -m32.
To make amends for the recent (temporary) testsuite failure
of my new gcc.target/i386/minmax-9.c when compiled with -m32,
this patch improves the -m32 code we generate for the examples
in that test case.
The trick is to expand smin(x,0) as "x < 0 ? x : 0" instead
of the current "x <= 0 ? x : 0", as the former can take
advantage of sign_bit_mask operations.
2020-08-10 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
* config/i386/i386-expand.c (ix86_expand_int_movcc): Expand
signed MIN_EXPR against zero as "x < 0 ? x : 0" instead of
"x <= 0 ? x : 0" to enable sign_bit_compare_p optimizations.
gcc/testsuite/ChangeLog
* gcc.target/i386/minmax-12.c: New test.
Diff:
---
gcc/config/i386/i386-expand.c | 12 +++++++++++-
gcc/testsuite/gcc.target/i386/minmax-12.c | 17 +++++++++++++++++
2 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/gcc/config/i386/i386-expand.c b/gcc/config/i386/i386-expand.c
index 1bd0df4daf4..f441ba929bc 100644
--- a/gcc/config/i386/i386-expand.c
+++ b/gcc/config/i386/i386-expand.c
@@ -3305,7 +3305,17 @@ ix86_expand_int_movcc (rtx operands[])
{
var = operands[2];
if (INTVAL (operands[3]) == 0 && operands[2] != constm1_rtx)
- operands[2] = constm1_rtx, op = and_optab;
+ {
+ /* For smin (x, 0), expand as "x < 0 ? x : 0" instead of
+ "x <= 0 ? x : 0" to enable sign_bit_compare_p. */
+ if (code == LE && op1 == const0_rtx && rtx_equal_p (op0, var))
+ operands[1] = simplify_gen_relational (LT, VOIDmode,
+ GET_MODE (op0),
+ op0, const0_rtx);
+
+ operands[2] = constm1_rtx;
+ op = and_optab;
+ }
else if (INTVAL (operands[3]) == -1 && operands[3] != const0_rtx)
operands[2] = const0_rtx, op = ior_optab;
else
diff --git a/gcc/testsuite/gcc.target/i386/minmax-12.c b/gcc/testsuite/gcc.target/i386/minmax-12.c
new file mode 100644
index 00000000000..40efe541e30
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/minmax-12.c
@@ -0,0 +1,17 @@
+/* { dg-do compile { target ia32 } } */
+/* { dg-options "-O2 -march=i386 -mtune=generic" } */
+
+#define min(a,b) (((a) < (b))? (a) : (b))
+
+int foo(int x)
+{
+ return min(x,0);
+}
+
+signed char bar(signed char x)
+{
+ return min(x,0);
+}
+
+/* { dg-final { scan-assembler "cltd" } } */
+/* { dg-final { scan-assembler "sarb" } } */
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