tor-browser

commit 9aa3304e2fa4134ff8306ee1a69a6f1b00cc3bc7
parent f6e86e9a5e2b3a964e777495238bced8cb2126e8
Author: André Bargull <andre.bargull@gmail.com>
Date:   Thu, 23 Oct 2025 09:56:06 +0000

Bug 1995488 - Part 2: Remove branches from clampDoubleToUint8 on riscv64. r=spidermonkey-reviewers,iain

Improves the generated code from:
```asm
feq.d     t4, ft1, ft1
beq       t4, zero, 0 -> nan
addi      zero, t4, 17
fcvt.w.d  [RNE] t0, ft1
sgtz      t5, t0
neg       t5, t5
and       t0, t0, t5
li        t5, 255
bge       t5, t0, 0 -> skip
li        t0, 255
j         0 -> done
mv        t0, zero
```

To:
```asm
fcvt.w.d  [RNE] t0, ft1
feq.d     t4, ft1, ft1
neg       t4, t4
and       t0, t0, t4
sgtz      t4, t0
neg       t4, t4
and       t0, t0, t4
li        t4, 255
bge       t4, t0, 0 -> skip
li        t0, 255
```

Two less instructions and only a single conditional jump.

Differential Revision: https://phabricator.services.mozilla.com/D269351

Diffstat:
M
js/src/jit/riscv64/MacroAssembler-riscv64.cpp
 | 
14
+-------------

1 file changed, 1 insertion(+), 13 deletions(-)
diff --git a/js/src/jit/riscv64/MacroAssembler-riscv64.cpp b/js/src/jit/riscv64/MacroAssembler-riscv64.cpp
@@ -2456,21 +2456,9 @@ void MacroAssembler::subFromStackPtr(Imm32 imm32) {
 }
 
 void MacroAssembler::clampDoubleToUint8(FloatRegister input, Register output) {
-  JitSpew(JitSpew_Codegen, "[ clampDoubleToUint8");
-  Label nan, done;
-  UseScratchRegisterScope temps(this);
-  Register scratch = temps.Acquire();
-  feq_d(scratch, input, input);
-  beqz(scratch, &nan);
-  addi(zero, scratch, 0x11);
   Round_w_d(output, input);
+  Clear_if_nan_d(output, input);
   clampIntToUint8(output);
-  ma_branch(&done);
-  // Input is nan
-  bind(&nan);
-  mv(output, zero_reg);
-  bind(&done);
-  JitSpew(JitSpew_Codegen, "]");
 }
 
 //{{{ check_macroassembler_style