RISC-V: Eliminate redundant zero extension of minu/maxu operands

RISC-V: Eliminate redundant zero extension of minu/maxu operands

[Jivan Hakobyan]

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RV64 the following code:

  unsigned Min(unsigned a, unsigned b) {
      return a < b ? a : b;
  }

Compiles to:
  Min:
       zext.w  a1,a1
       zext.w  a0,a0
       minu    a0,a1,a0
       sext.w  a0,a0
       ret

This patch removes unnecessary zero extensions of minu/maxu operands.

gcc/ChangeLog:

     * config/riscv/bitmanip.md: Added expanders for minu/maxu instructions

gcc/testsuite/ChangeLog:

   * gcc.target/riscv/zbb-min-max-02.c: Updated scanning check.
   * gcc.target/riscv/zbb-min-max-03.c: New tests.


--
With the best regards
Jivan Hakobyan

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diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index 44ad350c747..8580bb37ba0 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -401,7 +401,30 @@
   DONE;
 })
 
-(define_insn "<bitmanip_optab><mode>3"
+(define_expand "<bitmanip_optab>di3"
+  [(set (match_operand:DI 0 "register_operand" "=r")
+        (bitmanip_minmax:DI (match_operand:DI 1 "register_operand" "r")
+                            (match_operand:DI 2 "register_operand" "r")))]
+  "TARGET_64BIT && TARGET_ZBB")
+
+(define_expand "<bitmanip_optab>si3"
+  [(set (match_operand:SI 0 "register_operand" "=r")
+        (bitmanip_minmax:SI (match_operand:SI 1 "register_operand" "r")
+                            (match_operand:SI 2 "register_operand" "r")))]
+  "TARGET_ZBB"
+{
+  if (TARGET_64BIT)
+    {
+      rtx t = gen_reg_rtx (DImode);
+      operands[1] = force_reg (DImode, gen_rtx_SIGN_EXTEND (DImode, operands[1]));
+      operands[2] = force_reg (DImode, gen_rtx_SIGN_EXTEND (DImode, operands[2]));
+      emit_insn (gen_<bitmanip_optab>di3 (t, operands[1], operands[2]));
+      emit_move_insn (operands[0], gen_lowpart (SImode, t));
+      DONE;
+    }
+})
+
+(define_insn "*<bitmanip_optab><mode>3"
   [(set (match_operand:X 0 "register_operand" "=r")
         (bitmanip_minmax:X (match_operand:X 1 "register_operand" "r")
 			   (match_operand:X 2 "reg_or_0_operand" "rJ")))]
diff --git a/gcc/testsuite/gcc.target/riscv/zbb-min-max-02.c b/gcc/testsuite/gcc.target/riscv/zbb-min-max-02.c
index b462859f10f..edfbf807d45 100644
--- a/gcc/testsuite/gcc.target/riscv/zbb-min-max-02.c
+++ b/gcc/testsuite/gcc.target/riscv/zbb-min-max-02.c
@@ -1,6 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-march=rv64gc_zba_zbb -mabi=lp64" } */
-/* { dg-skip-if "" { *-*-* } { "-O0" "-O1" "-Os" "-Oz" "-Og" } } */
+/* { dg-skip-if "" { *-*-* } { "-O0" } } */
 
 int f(unsigned int* a)
 {
@@ -9,6 +9,6 @@ int f(unsigned int* a)
 }
 
 /* { dg-final { scan-assembler-times "minu" 1 } } */
-/* { dg-final { scan-assembler-times "sext.w" 1 } } */
+/* { dg-final { scan-assembler-not "sext.w" } } */
 /* { dg-final { scan-assembler-not "zext.w" } } */
 
diff --git a/gcc/testsuite/gcc.target/riscv/zbb-min-max-03.c b/gcc/testsuite/gcc.target/riscv/zbb-min-max-03.c
index c7de1004048..38c932b9580 100644
--- a/gcc/testsuite/gcc.target/riscv/zbb-min-max-03.c
+++ b/gcc/testsuite/gcc.target/riscv/zbb-min-max-03.c
@@ -6,5 +6,18 @@ int f(int x) {
  return x >= 0 ? x : 0;
 }
 
+unsigned f2(unsigned x, unsigned y) {
+  return x > y ? x : y;
+}
+
+unsigned f3(unsigned x, unsigned y) {
+  return x < y ? x : y;
+}
+
 /* { dg-final { scan-assembler-times "max\t" 1 } } */
 /* { dg-final { scan-assembler-not "li\t" } } */
+/* { dg-final { scan-assembler-times "maxu\t" 1 } } */
+/* { dg-final { scan-assembler-times "minu\t" 1 } } */
+/* { dg-final { scan-assembler-not "zext.w" } } */
+/* { dg-final { scan-assembler-not "sext.w" } } */
+

Re: RISC-V: Eliminate redundant zero extension of minu/maxu operands

[Jeff Law]

On 4/28/23 06:29, Jivan Hakobyan via Gcc-patches wrote:
> RV64 the following code:
> 
>    unsigned Min(unsigned a, unsigned b) {
>        return a < b ? a : b;
>    }
> 
> Compiles to:
>    Min:
>         zext.w  a1,a1
>         zext.w  a0,a0
>         minu    a0,a1,a0
>         sext.w  a0,a0
>         ret
> 
> This patch removes unnecessary zero extensions of minu/maxu operands.
> 
> gcc/ChangeLog:
> 
>       * config/riscv/bitmanip.md: Added expanders for minu/maxu instructions
> 
> gcc/testsuite/ChangeLog:
> 
>     * gcc.target/riscv/zbb-min-max-02.c: Updated scanning check.
>     * gcc.target/riscv/zbb-min-max-03.c: New tests.
Thanks.  We had almost the exact same patch internally, the differences 
were just in naming rather than anything functional.  I went ahead and 
installed your variant and I'll drop Raphael's from my queue.

I realize this may make some planned work WRT eliminating unnecessary 
extensions in gimple somewhat harder.  If that work progresses to the 
point where this patch is a problem, then we'll re-evaluate.  But it's 
crazy to hold this up -- it's a measurable win on x264 in particular.

Thanks again,
jeff