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Cranelift: implicitly consider trapping blocks as "cold" during lowering #13689

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Merged
fitzgen merged 2 commits into from
Jun 18, 2026
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Cranelift: implicitly consider trapping blocks as "cold" during lowering #13689

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8e14271
Cranelift: implicitly consider trapping blocks as "cold" during lowering
fitzgen Jun 18, 2026
c71e7ff
Add an `ir::Function::is_effectively_cold` method
fitzgen Jun 18, 2026
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14 changes: 14 additions & 0 deletions cranelift/codegen/src/ir/function.rs
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Expand Up @@ -473,6 +473,20 @@ impl Function {
pub fn import_function(&mut self, data: ExtFuncData) -> FuncRef {
self.stencil.dfg.ext_funcs.push(data)
}

/// Is the given block marked `cold` or otherwise effectively `cold` in
/// practice?
pub fn is_effectively_cold(&self, block: Block) -> bool {
if self.layout.is_cold(block) {
return true;
}

// Blocks that unconditionally trap are effectively
// also cold.
self.layout
.last_inst(block)
.is_some_and(|inst| self.dfg.insts[inst].opcode() == ir::Opcode::Trap)
}
}

/// Wrapper type capable of displaying a `Function`.
Expand Down
4 changes: 2 additions & 2 deletions cranelift/codegen/src/machinst/blockorder.rs
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Expand Up @@ -257,7 +257,7 @@ impl BlockLoweringOrder {
lowered_succ_indices
.extend(block_succs[range].iter().map(|lb| lb_to_bindex[lb]));

if f.layout.is_cold(block) {
if f.is_effectively_cold(block) {
cold_blocks.insert(bindex);
}

Expand All @@ -282,7 +282,7 @@ impl BlockLoweringOrder {
// Edges inherit indirect branch and cold block metadata from their
// successor.

if f.layout.is_cold(succ) {
if f.is_effectively_cold(succ) {
cold_blocks.insert(bindex);
}

Expand Down
40 changes: 40 additions & 0 deletions cranelift/filetests/filetests/isa/pulley64/trap_blocks_are_cold.clif
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@@ -0,0 +1,40 @@
test compile precise-output
target pulley64

function %f(i8, i64) -> i64 {
block0(v0: i8, v1: i64):
brif v0, block1, block2

;; This block is implicitly cold because it ends in a trap; it should come last
;; in the lowered block order.
block1:
v2 = iconst.i32 42
store notrap aligned v2, v1
trap user123

block2:
v3 = iconst.i64 0
return v3
}

; VCode:
; block0:
; zext8 x5, x0
; br_if32 x5, label2; jump label1
; block1:
; xzero x0
; ret
; block2:
; xconst8 x7, 42
; xstore32 x1+0, x7 // flags = notrap aligned
; trap // trap=TrapCode(123)
;
; Disassembled:
; zext8 x5, x0
; br_if32 x5, 0x9 // target = 0xc
; xzero x0
; ret
; xconst8 x7, 42
; xstore32le_o32 x1, 0, x7
; trap

119 changes: 60 additions & 59 deletions tests/disas/debug-exceptions.wat
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Original file line number Diff line number Diff line change
Expand Up @@ -31,35 +31,35 @@
;; stur x0, [sp, #0x18]
;; mov x0, sp
;; cmp x0, x1
;; b.lo #0x21c
;; b.lo #0x220
;; 48: stur x2, [sp]
;; mov x0, x2
;; stur x2, [sp, #0x10]
;; nop
;; ├─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x35, slot at FP-0xb0, locals , stack
;; ╰─╼ breakpoint patch: wasm PC 0x35, patch bytes [61, 1, 0, 148]
;; ╰─╼ breakpoint patch: wasm PC 0x35, patch bytes [62, 1, 0, 148]
;; ldur x0, [sp, #0x10]
;; nop
;; ├─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x37, slot at FP-0xb0, locals , stack
;; ╰─╼ breakpoint patch: wasm PC 0x37, patch bytes [59, 1, 0, 148]
;; ╰─╼ breakpoint patch: wasm PC 0x37, patch bytes [60, 1, 0, 148]
;; ldur x0, [sp, #0x10]
;; nop
;; ├─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x3d, slot at FP-0xb0, locals , stack
;; ╰─╼ breakpoint patch: wasm PC 0x3d, patch bytes [57, 1, 0, 148]
;; ╰─╼ breakpoint patch: wasm PC 0x3d, patch bytes [58, 1, 0, 148]
;; mov w1, #0x2a
;; stur w1, [sp, #8]
;; nop
;; ├─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x3f, slot at FP-0xb0, locals , stack I32 @ slot+0x8
;; ╰─╼ breakpoint patch: wasm PC 0x3f, patch bytes [54, 1, 0, 148]
;; ╰─╼ breakpoint patch: wasm PC 0x3f, patch bytes [55, 1, 0, 148]
;; nop
;; ├─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x40, slot at FP-0xb0, locals , stack
;; ╰─╼ breakpoint patch: wasm PC 0x40, patch bytes [53, 1, 0, 148]
;; ╰─╼ breakpoint patch: wasm PC 0x40, patch bytes [54, 1, 0, 148]
;; stur w1, [sp, #8]
;; nop
;; ├─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x42, slot at FP-0xb0, locals , stack I32 @ slot+0x8
;; ╰─╼ breakpoint patch: wasm PC 0x42, patch bytes [51, 1, 0, 148]
;; ╰─╼ breakpoint patch: wasm PC 0x42, patch bytes [52, 1, 0, 148]
;; ldur x2, [sp, #0x10]
;; bl #0x4b0
;; bl #0x4b4
;; 88: ldur x0, [sp, #0x10]
;; mov x19, x2
;; ldr x1, [x0, #0x20]
Expand All @@ -68,7 +68,7 @@
;; add x2, x2, #0x20
;; ldr w4, [x1, #4]
;; cmp x2, x4
;; b.hi #0x1b4
;; b.hi #0x1a0
;; ac: ldur x0, [sp, #0x18]
;; add w4, w3, #0x20
;; str w4, [x1]
Expand All @@ -92,47 +92,41 @@
;; mov w11, #0
;; str w11, [x1, #0x14]
;; ldur x2, [sp, #0x10]
;; bl #0x4e8
;; bl #0x4ec
;; ├─╼ exception frame offset: SP = FP - 0xb0
;; ╰─╼ exception handler: tag=0, context at [SP+0x10], handler=0x124
;; 10c: mov w3, #9
;; ldur x2, [sp, #0x10]
;; bl #0x444
;; 118: ldur x2, [sp, #0x10]
;; bl #0x47c
;; ╰─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x42, slot at FP-0xb0, locals , stack I32 @ slot+0x8
;; 120: udf #0xc11f
;; mov w1, w0
;; ╰─╼ exception handler: tag=0, context at [SP+0x10], handler=0x110
;; b #0x1d8
;; 110: mov w1, w0
;; mov x2, #0x20
;; adds x15, x1, x2
;; cset x1, hs
;; tst w1, #0xff
;; b.ne #0x204
;; 13c: ldur x2, [sp, #0x18]
;; b.ne #0x208
;; 128: ldur x2, [sp, #0x18]
;; ldr x1, [x2, #0x28]
;; cmp x15, x1
;; b.hi #0x1ec
;; 14c: ldr x1, [x2, #0x20]
;; b.hi #0x1f0
;; 138: ldr x1, [x2, #0x20]
;; add x1, x1, #0x18
;; ldr w0, [x1, w0, uxtw]
;; stur w0, [sp, #8]
;; ldur x0, [sp, #0x10]
;; nop
;; ├─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x48, slot at FP-0xb0, locals , stack I32 @ slot+0x8
;; ╰─╼ breakpoint patch: wasm PC 0x48, patch bytes [250, 0, 0, 148]
;; ╰─╼ breakpoint patch: wasm PC 0x48, patch bytes [0, 1, 0, 148]
;; ldur x1, [sp, #0x10]
;; ldr x0, [x1, #0x38]
;; ldr x2, [x1, #0x48]
;; ldur x3, [sp, #0x10]
;; blr x0
;; ╰─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x4a, slot at FP-0xb0, locals , stack I32 @ slot+0x8
;; 178: ldur x0, [sp, #0x10]
;; 164: ldur x0, [sp, #0x10]
;; nop
;; ├─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x4a, slot at FP-0xb0, locals , stack I32 @ slot+0x8
;; ╰─╼ breakpoint patch: wasm PC 0x4a, patch bytes [243, 0, 0, 148]
;; ╰─╼ breakpoint patch: wasm PC 0x4a, patch bytes [249, 0, 0, 148]
;; nop
;; ├─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x4b, slot at FP-0xb0, locals , stack
;; ╰─╼ breakpoint patch: wasm PC 0x4b, patch bytes [242, 0, 0, 148]
;; ╰─╼ breakpoint patch: wasm PC 0x4b, patch bytes [248, 0, 0, 148]
;; add sp, sp, #0x20
;; ldp d8, d9, [sp], #0x10
;; ldp d10, d11, [sp], #0x10
Expand All @@ -145,38 +139,45 @@
;; ldp x27, x28, [sp], #0x10
;; ldp x29, x30, [sp], #0x10
;; ret
;; 1b4: mov w3, #2
;; 1b8: movk w3, #0x400, lsl #16
;; 1bc: ldur x0, [sp, #0x10]
;; 1c0: ldr x4, [x0, #0x28]
;; 1c4: ldr w4, [x4, #8]
;; 1c8: mov w5, #0x20
;; 1cc: mov w6, #0x10
;; 1d0: ldur x2, [sp, #0x10]
;; 1d4: bl #0x3dc
;; 1d8: ldur x0, [sp, #0x18]
;; 1dc: ldr x3, [x0, #0x20]
;; 1e0: add x1, x3, w2, uxtw
;; 1e4: mov x3, x2
;; 1e8: b #0xec
;; 1ec: mov w3, #0xfe
;; 1f0: ldur x2, [sp, #0x10]
;; 1f4: bl #0x444
;; 1f8: ldur x2, [sp, #0x10]
;; 1fc: bl #0x47c
;; 1a0: mov w3, #2
;; 1a4: movk w3, #0x400, lsl #16
;; 1a8: ldur x0, [sp, #0x10]
;; 1ac: ldr x4, [x0, #0x28]
;; 1b0: ldr w4, [x4, #8]
;; 1b4: mov w5, #0x20
;; 1b8: mov w6, #0x10
;; 1bc: ldur x2, [sp, #0x10]
;; 1c0: bl #0x3e0
;; 1c4: ldur x0, [sp, #0x18]
;; 1c8: ldr x3, [x0, #0x20]
;; 1cc: add x1, x3, w2, uxtw
;; 1d0: mov x3, x2
;; 1d4: b #0xec
;; 1d8: mov w3, #9
;; 1dc: ldur x2, [sp, #0x10]
;; 1e0: bl #0x448
;; 1e4: ldur x2, [sp, #0x10]
;; 1e8: bl #0x480
;; ╰─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x42, slot at FP-0xb0, locals , stack I32 @ slot+0x8
;; 1ec: udf #0xc11f
;; 1f0: mov w3, #0xfe
;; 1f4: ldur x2, [sp, #0x10]
;; 1f8: bl #0x448
;; 1fc: ldur x2, [sp, #0x10]
;; 200: bl #0x480
;; ╰─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x37, slot at FP-0xb0, locals , stack
;; 200: udf #0xc11f
;; 204: mov w3, #0xfe
;; 208: ldur x2, [sp, #0x10]
;; 20c: bl #0x444
;; 210: ldur x2, [sp, #0x10]
;; 214: bl #0x47c
;; 204: udf #0xc11f
;; 208: mov w3, #0xfe
;; 20c: ldur x2, [sp, #0x10]
;; 210: bl #0x448
;; 214: ldur x2, [sp, #0x10]
;; 218: bl #0x480
;; ╰─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x37, slot at FP-0xb0, locals , stack
;; 218: udf #0xc11f
;; 21c: stur x2, [sp, #0x10]
;; 220: mov w3, #0
;; 224: bl #0x444
;; 228: ldur x2, [sp, #0x10]
;; 22c: bl #0x47c
;; 21c: udf #0xc11f
;; 220: stur x2, [sp, #0x10]
;; 224: mov w3, #0
;; 228: bl #0x448
;; 22c: ldur x2, [sp, #0x10]
;; 230: bl #0x480
;; ╰─╼ debug frame state (after previous inst): func key DefinedWasmFunction(StaticModuleIndex(0), DefinedFuncIndex(0)), wasm PC 0x34, slot at FP-0xb0, locals , stack
;; 230: udf #0xc11f
;; 234: udf #0xc11f
11 changes: 6 additions & 5 deletions tests/disas/exceptions.wat
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Expand Up @@ -23,7 +23,7 @@
;; movq 0x18(%r10), %r10
;; addq $0x50, %r10
;; cmpq %rsp, %r10
;; ja 0xe7
;; ja 0xec
;; 19: subq $0x40, %rsp
;; movq %rbx, 0x10(%rsp)
;; movq %r12, 0x18(%rsp)
Expand All @@ -41,7 +41,7 @@
;; leaq 0x30(%rcx), %rax
;; movl 4(%rdx), %edi
;; cmpq %rdi, %rax
;; ja 0xb3
;; ja 0xb6
;; 5f: leal 0x30(%rsi), %eax
;; movl %eax, (%rdx)
;; movq 8(%rbx), %rax
Expand All @@ -63,8 +63,8 @@
;; movq %rbx, %rdi
;; movq %rbx, (%rsp)
;; callq 0x418
;; ud2
;; movl $0x4000002, %esi
;; jmp 0xea
;; b6: movl $0x4000002, %esi
;; movq 0x28(%rbx), %rax
;; movl 0xc(%rax), %edx
;; movl $0x30, %ecx
Expand All @@ -77,7 +77,8 @@
;; movq %rax, %rsi
;; movq %r14, %rdi
;; jmp 0x8e
;; e7: ud2
;; ea: ud2
;; ud2
;;
;; wasm[0]::function[1]::catch:
;; pushq %rbp
Expand Down
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