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wcc: float arr[i]= spills X0 across index eval (#125)

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Fix value-loss bug introduced as a #122 boundary in the float
arr[i]=v store: when the index sub-expr clobbers X0 (e.g.
`a[geti()]=1.5f32`), the value is lost. Mirror the scalar-deref
X0-spill template (cstage cgen.c:4187; line shifted from the brief's
stale :3859 cite by intervening #133/#135/#138 commits): for float
element only, replace PUSHQ AX (junk for floats — value is in X0)
with SUBQ $8,SP + MOVSS/MOVSD X0,(SP) before the idx/base eval;
mirror replace POPQ AX with MOVSS/MOVSD (SP),X0 + ADDQ $8,SP after.
Wwstage parallel. Non-float keeps PUSHQ/POPQ AX so the str/slice
3-word {ptr,len,cap} pop order at the end of the branch is preserved.
#122 trailing-store comment updated from "Deferred to #125" to a
positive cite.

Test 916: 5 rows — f64_call_index + f32_call_index canonical repros
(geti's body clobbers X0; pre-fix exit=2 from post-call residue,
post-fix exit=1 from the spilled 1.5) + f64_lit_index / _localvar /
_arith control rows for non-X0-clobbering index paths. f32_call_index
uses an int-arg call to dodge the sibling cs/ww f32-arg-push
MOVSD-vs-MOVSS divergence (#143, task #36 — orthogonal, filed).

Bootstrap NEUTRAL (zero current float arr[i]= callers in lib; only
[N]u8 byte-buffers like f64tos_buf). cs==ww byte-identical both
stages (990-997 + 916 inline cmp). Closes the #122 boundary-doc
loose end; completes the #122 family.
This commit is contained in:
Hojun-Cho
2026-05-27 03:30:15 +09:00
parent 1de1b9a8a9
commit 61e6aab384
6 changed files with 362 additions and 29 deletions
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37
selfhost/cmd/w6c/main.combined.ww
View File

@@ -19001,7 +19001,22 @@ fn cgassign(c: *cgen, n: *node) void = {
emitline("\tPUSHQ\tCX\n");
emitline("\tPUSHQ\tBX\n");
};
emitline("\tPUSHQ\tAX\n");
// Float element: spill X0 (not AX — AX is junk for
// floats) across the idx/base eval. A call-index
// (a[geti()]=v) clobbers X0 and would otherwise lose
// the value. Mirrors the *p=v float deref store
// twin in cgassign (#125).
let spisfloat: bool = isfloattype(c, elemtn);
let spmov: str = "MOVSD";
if (isf32type(c, elemtn)) { spmov = "MOVSS"; };
if (spisfloat) {
emitline("\tSUBQ\t$8, SP\n");
emitline("\t");
emitline(spmov);
emitline("\tX0, (SP)\n");
} else {
emitline("\tPUSHQ\tAX\n");
};
cgexpr(c, idx); // idx → AX
if (esz > 1) {
emitline("\tMOVQ\t$");
@@ -19039,7 +19054,17 @@ fn cgassign(c: *cgen, n: *node) void = {
};};};};
emitline("\tPOPQ\tAX\n"); // scaled idx
emitline("\tADDQ\tAX, BX\n");
emitline("\tPOPQ\tAX\n"); // value
// Reload value: float reloads X0 from the spill slot;
// non-float pops AX. Twin of the value-spill site
// above (#125).
if (spisfloat) {
emitline("\t");
emitline(spmov);
emitline("\t(SP), X0\n");
emitline("\tADDQ\t$8, SP\n");
} else {
emitline("\tPOPQ\tAX\n"); // value
};
// str/slice: pop the saved len + cap and store
// all three words. Kind-gate, not size — see the
// spill site above (#1/Phase 3, #7/754).
@@ -19052,11 +19077,9 @@ fn cgassign(c: *cgen, n: *node) void = {
return;
};
// float element → store FROM X0 (MOVSS/MOVSD): cgexpr
// left the value in X0. X0 survives the index/base
// eval only for literal/local-var indices; a call-
// index (a[geti()]=v) clobbers X0 and loses the value
// — this path does not spill X0 across the eval,
// unlike the *p=v float deref store. Deferred to #125.
// left the value in X0, and the value-spill pair
// above keeps X0 live across the idx/base eval so
// a call-index (a[geti()]=v) doesn't lose it (#125).
// For f32 the #104 CVTSD2SS narrowing only touches X0,
// so the AX store below would write raw double low-
// bits, garbage for f32 (#122, mirrors cstage cgen.c

37
selfhost/cmd/wcc/cgenexpr.ww
View File

@@ -4382,7 +4382,22 @@ fn cgassign(c: *cgen, n: *node) void = {
emitline("\tPUSHQ\tCX\n");
emitline("\tPUSHQ\tBX\n");
};
emitline("\tPUSHQ\tAX\n");
// Float element: spill X0 (not AX — AX is junk for
// floats) across the idx/base eval. A call-index
// (a[geti()]=v) clobbers X0 and would otherwise lose
// the value. Mirrors the *p=v float deref store
// twin in cgassign (#125).
let spisfloat: bool = isfloattype(c, elemtn);
let spmov: str = "MOVSD";
if (isf32type(c, elemtn)) { spmov = "MOVSS"; };
if (spisfloat) {
emitline("\tSUBQ\t$8, SP\n");
emitline("\t");
emitline(spmov);
emitline("\tX0, (SP)\n");
} else {
emitline("\tPUSHQ\tAX\n");
};
cgexpr(c, idx); // idx → AX
if (esz > 1) {
emitline("\tMOVQ\t$");
@@ -4420,7 +4435,17 @@ fn cgassign(c: *cgen, n: *node) void = {
};};};};
emitline("\tPOPQ\tAX\n"); // scaled idx
emitline("\tADDQ\tAX, BX\n");
emitline("\tPOPQ\tAX\n"); // value
// Reload value: float reloads X0 from the spill slot;
// non-float pops AX. Twin of the value-spill site
// above (#125).
if (spisfloat) {
emitline("\t");
emitline(spmov);
emitline("\t(SP), X0\n");
emitline("\tADDQ\t$8, SP\n");
} else {
emitline("\tPOPQ\tAX\n"); // value
};
// str/slice: pop the saved len + cap and store
// all three words. Kind-gate, not size — see the
// spill site above (#1/Phase 3, #7/754).
@@ -4433,11 +4458,9 @@ fn cgassign(c: *cgen, n: *node) void = {
return;
};
// float element → store FROM X0 (MOVSS/MOVSD): cgexpr
// left the value in X0. X0 survives the index/base
// eval only for literal/local-var indices; a call-
// index (a[geti()]=v) clobbers X0 and loses the value
// — this path does not spill X0 across the eval,
// unlike the *p=v float deref store. Deferred to #125.
// left the value in X0, and the value-spill pair
// above keeps X0 live across the idx/base eval so
// a call-index (a[geti()]=v) doesn't lose it (#125).
// For f32 the #104 CVTSD2SS narrowing only touches X0,
// so the AX store below would write raw double low-
// bits, garbage for f32 (#122, mirrors cstage cgen.c

37
selfhost/cmd/wwdump/main.combined.ww
View File

@@ -19001,7 +19001,22 @@ fn cgassign(c: *cgen, n: *node) void = {
emitline("\tPUSHQ\tCX\n");
emitline("\tPUSHQ\tBX\n");
};
emitline("\tPUSHQ\tAX\n");
// Float element: spill X0 (not AX — AX is junk for
// floats) across the idx/base eval. A call-index
// (a[geti()]=v) clobbers X0 and would otherwise lose
// the value. Mirrors the *p=v float deref store
// twin in cgassign (#125).
let spisfloat: bool = isfloattype(c, elemtn);
let spmov: str = "MOVSD";
if (isf32type(c, elemtn)) { spmov = "MOVSS"; };
if (spisfloat) {
emitline("\tSUBQ\t$8, SP\n");
emitline("\t");
emitline(spmov);
emitline("\tX0, (SP)\n");
} else {
emitline("\tPUSHQ\tAX\n");
};
cgexpr(c, idx); // idx → AX
if (esz > 1) {
emitline("\tMOVQ\t$");
@@ -19039,7 +19054,17 @@ fn cgassign(c: *cgen, n: *node) void = {
};};};};
emitline("\tPOPQ\tAX\n"); // scaled idx
emitline("\tADDQ\tAX, BX\n");
emitline("\tPOPQ\tAX\n"); // value
// Reload value: float reloads X0 from the spill slot;
// non-float pops AX. Twin of the value-spill site
// above (#125).
if (spisfloat) {
emitline("\t");
emitline(spmov);
emitline("\t(SP), X0\n");
emitline("\tADDQ\t$8, SP\n");
} else {
emitline("\tPOPQ\tAX\n"); // value
};
// str/slice: pop the saved len + cap and store
// all three words. Kind-gate, not size — see the
// spill site above (#1/Phase 3, #7/754).
@@ -19052,11 +19077,9 @@ fn cgassign(c: *cgen, n: *node) void = {
return;
};
// float element → store FROM X0 (MOVSS/MOVSD): cgexpr
// left the value in X0. X0 survives the index/base
// eval only for literal/local-var indices; a call-
// index (a[geti()]=v) clobbers X0 and loses the value
// — this path does not spill X0 across the eval,
// unlike the *p=v float deref store. Deferred to #125.
// left the value in X0, and the value-spill pair
// above keeps X0 live across the idx/base eval so
// a call-index (a[geti()]=v) doesn't lose it (#125).
// For f32 the #104 CVTSD2SS narrowing only touches X0,
// so the AX store below would write raw double low-
// bits, garbage for f32 (#122, mirrors cstage cgen.c