commit 453e8da7933f7e61dbc03ee2a6a91e2b548809c2
parent 5dbd7fb9849c51326867794fcf3bfd0bc55b8640
Author: André Bargull <andre.bargull@gmail.com>
Date: Fri, 17 Oct 2025 11:25:45 +0000
Bug 1994191 - Part 1: Clean-up riscv branching code. r=spidermonkey-reviewers,iain
Changes:
- Avoid loading zero immediate into a register.
- Remove duplicate code in `ma_branch`.
- Always try short jumps in `ma_branch` if the label is already bound.
Differential Revision: https://phabricator.services.mozilla.com/D268550
Diffstat:
2 files changed, 57 insertions(+), 60 deletions(-)
diff --git a/js/src/jit/riscv64/Assembler-riscv64.h b/js/src/jit/riscv64/Assembler-riscv64.h
@@ -497,8 +497,6 @@ class Assembler : public AssemblerShared,
return &scratch_register_list_;
}
- void EmitConstPoolWithJumpIfNeeded(size_t margin = 0) {}
-
// As opposed to x86/x64 version, the data relocation has to be executed
// before to recover the pointer, and not after.
void writeDataRelocation(ImmGCPtr ptr) {
diff --git a/js/src/jit/riscv64/MacroAssembler-riscv64.cpp b/js/src/jit/riscv64/MacroAssembler-riscv64.cpp
@@ -4918,8 +4918,12 @@ bool MacroAssemblerRiscv64::BranchShortHelper(int32_t offset, Label* L,
UseScratchRegisterScope temps(this);
Register scratch = Register();
if (rt.is_imm()) {
- scratch = temps.Acquire();
- ma_li(scratch, Imm64(rt.immediate()));
+ if (rt.immediate() == 0) {
+ scratch = zero;
+ } else {
+ scratch = temps.Acquire();
+ ma_li(scratch, Imm64(rt.immediate()));
+ }
} else {
MOZ_ASSERT(rt.is_reg());
scratch = rt.rm();
@@ -4930,7 +4934,6 @@ bool MacroAssemblerRiscv64::BranchShortHelper(int32_t offset, Label* L,
case Always:
if (!CalculateOffset(L, &offset, OffsetSize::kOffset21)) return false;
Assembler::j(offset);
- EmitConstPoolWithJumpIfNeeded();
break;
case Equal:
// rs == rt
@@ -5073,15 +5076,13 @@ void MacroAssemblerRiscv64::BranchLong(Label* L) {
// Generate position independent long branch.
UseScratchRegisterScope temps(this);
Register scratch = temps.Acquire();
- int32_t imm;
- imm = branch_long_offset(L);
+ int32_t imm = branch_long_offset(L);
GenPCRelativeJump(scratch, imm);
}
void MacroAssemblerRiscv64::BranchAndLinkLong(Label* L) {
// Generate position independent long branch and link.
- int32_t imm;
- imm = branch_long_offset(L);
+ int32_t imm = branch_long_offset(L);
UseScratchRegisterScope temps(this);
Register scratch = temps.Acquire();
GenPCRelativeJumpAndLink(scratch, imm);
@@ -5089,37 +5090,25 @@ void MacroAssemblerRiscv64::BranchAndLinkLong(Label* L) {
void MacroAssemblerRiscv64::ma_branch(Label* L, Condition cond, Register rs,
const Operand& rt, JumpKind jumpKind) {
- if (L->used()) {
- if (jumpKind == ShortJump && BranchShortCheck(0, L, cond, rs, rt)) {
- return;
- }
- if (cond != Always) {
- Label skip;
- Condition neg_cond = InvertCondition(cond);
- (void)BranchShort(&skip, neg_cond, rs, rt); // Guaranteed to be short.
- BranchLong(L);
- bind(&skip);
- } else {
- BranchLong(L);
- EmitConstPoolWithJumpIfNeeded();
- }
+ // Always prefer short jumps when the label is already bound. (If the label is
+ // bound, BranchShort can cheaply determine if short jumps are possible.)
+ if (L->bound()) {
+ jumpKind = ShortJump;
+ }
+
+ if (jumpKind == ShortJump && BranchShort(L, cond, rs, rt)) {
+ return;
+ }
+
+ if (cond != Always) {
+ Label skip;
+ Condition neg_cond = InvertCondition(cond);
+ MOZ_ALWAYS_TRUE(
+ BranchShort(&skip, neg_cond, rs, rt)); // Guaranteed to be short.
+ BranchLong(L);
+ bind(&skip);
} else {
- if (jumpKind == LongJump) {
- if (cond != Always) {
- Label skip;
- Condition neg_cond = InvertCondition(cond);
- (void)BranchShort(&skip, neg_cond, rs, rt); // Guaranteed to be short.
- BranchLong(L);
- bind(&skip);
- } else {
- BranchLong(L);
- EmitConstPoolWithJumpIfNeeded();
- }
- } else {
- if (!BranchShort(L, cond, rs, rt)) {
- ma_branch(L, cond, rs, rt, LongJump);
- }
- }
+ BranchLong(L);
}
}
@@ -5138,27 +5127,42 @@ void MacroAssemblerRiscv64::ma_b(Register lhs, ImmPtr imm, Label* l,
ma_b(lhs, ImmWord(uintptr_t(imm.value)), l, c, jumpKind);
}
-// Branches when done from within loongarch-specific code.
+// Branches when done from within riscv code.
void MacroAssemblerRiscv64::ma_b(Register lhs, ImmWord imm, Label* label,
Condition c, JumpKind jumpKind) {
- UseScratchRegisterScope temps(this);
- Register scratch = temps.Acquire();
- MOZ_ASSERT(lhs != scratch);
- ma_li(scratch, imm);
- ma_b(lhs, Register(scratch), label, c, jumpKind);
+ switch (c) {
+ case Always:
+ ma_branch(label, c, zero, Operand(zero), jumpKind);
+ break;
+ case Zero:
+ case NonZero:
+ case Signed:
+ case NotSigned:
+ MOZ_ASSERT(imm.value == 0);
+ ma_b(lhs, lhs, label, c, jumpKind);
+ break;
+ default:
+ ma_branch(label, c, lhs, Operand(imm.value), jumpKind);
+ break;
+ }
}
void MacroAssemblerRiscv64::ma_b(Register lhs, Imm32 imm, Label* label,
Condition c, JumpKind jumpKind) {
- if ((c == NonZero || c == Zero || c == Signed || c == NotSigned) &&
- imm.value == 0) {
- ma_b(lhs, lhs, label, c, jumpKind);
- } else {
- UseScratchRegisterScope temps(this);
- Register scratch = temps.Acquire();
- MOZ_ASSERT(lhs != scratch);
- ma_li(scratch, imm);
- ma_b(lhs, Register(scratch), label, c, jumpKind);
+ switch (c) {
+ case Always:
+ ma_branch(label, c, zero, Operand(zero), jumpKind);
+ break;
+ case Zero:
+ case NonZero:
+ case Signed:
+ case NotSigned:
+ MOZ_ASSERT(imm.value == 0);
+ ma_b(lhs, lhs, label, c, jumpKind);
+ break;
+ default:
+ ma_branch(label, c, lhs, Operand(imm.value), jumpKind);
+ break;
}
}
@@ -5173,10 +5177,6 @@ void MacroAssemblerRiscv64::ma_b(Address addr, Imm32 imm, Label* label,
void MacroAssemblerRiscv64::ma_b(Register lhs, Register rhs, Label* label,
Condition c, JumpKind jumpKind) {
switch (c) {
- case Equal:
- case NotEqual:
- ma_branch(label, c, lhs, rhs, jumpKind);
- break;
case Always:
ma_branch(label, c, zero, Operand(zero), jumpKind);
break;
@@ -5196,10 +5196,9 @@ void MacroAssemblerRiscv64::ma_b(Register lhs, Register rhs, Label* label,
MOZ_ASSERT(lhs == rhs);
ma_branch(label, GreaterThanOrEqual, lhs, Operand(zero), jumpKind);
break;
- default: {
+ default:
ma_branch(label, c, lhs, rhs, jumpKind);
break;
- }
}
}
