Don't leave debug locations for constants sitting on the builder indefinitely

[khuey]

Because constants are currently emitted before the prologue, leaving the debug location on the IRBuilder spills onto other instructions in the prologue and messes up both line numbers as well as the point LLVM chooses to be the prologue end.

Example LLVM IR (irrelevant IR elided):
Before:

define internal { i64, i64 } @_ZN3tmp3Foo18var_return_opt_try17he02116165b0fc08cE(ptr align 8 %self) !dbg !347 { start:
  %self.dbg.spill = alloca [8 x i8], align 8
  %_0 = alloca [16 x i8], align 8
  %residual.dbg.spill = alloca [0 x i8], align 1
    #dbg_declare(ptr %residual.dbg.spill, !353, !DIExpression(), !357)
  store ptr %self, ptr %self.dbg.spill, align 8, !dbg !357
    #dbg_declare(ptr %self.dbg.spill, !350, !DIExpression(), !358)

After:

define internal { i64, i64 } @_ZN3tmp3Foo18var_return_opt_try17h00b17d08874ddd90E(ptr align 8 %self) !dbg !347 { start:
  %self.dbg.spill = alloca [8 x i8], align 8
  %_0 = alloca [16 x i8], align 8
  %residual.dbg.spill = alloca [0 x i8], align 1
    #dbg_declare(ptr %residual.dbg.spill, !353, !DIExpression(), !357)
  store ptr %self, ptr %self.dbg.spill, align 8
    #dbg_declare(ptr %self.dbg.spill, !350, !DIExpression(), !358)

Note in particular how !357 from %residual.dbg.spill's dbg_declare no longer falls through onto the store to %self.dbg.spill. This fixes argument values at entry when the constant is a ZST (e.g. <Option as Try>::Residual). This fixes #130003 (but note that it does not fix issues with argument values and non-ZST constants, which emit their own stores that have debug info on them, like #128945).

r? @michaelwoerister

[rustbot]

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

[michaelwoerister]

Thanks, @khuey! Looks good to me.
@bors r+

[bors]

📌 Commit 7ed9f94 has been approved by michaelwoerister

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7ed9f94 with merge 5e84295...

[bors]

☀️ Test successful - checks-actions
Approved by: michaelwoerister
Pushing 5e84295 to master...

[rust-timer]

Finished benchmarking commit (5e84295): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.4%	[-1.4%, -1.4%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -3.2%, secondary -2.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.2%	[-3.5%, -2.9%]	2
Improvements ✅ (secondary)	-2.1%	[-3.6%, -1.2%]	4
All ❌✅ (primary)	-3.2%	[-3.5%, -2.9%]	2

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

Results (primary -0.2%, secondary -0.4%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.6%, -0.0%]	50
Improvements ✅ (secondary)	-0.4%	[-1.1%, -0.1%]	15
All ❌✅ (primary)	-0.2%	[-0.6%, -0.0%]	50

Bootstrap: 756.26s -> 757.063s (0.11%)
Artifact size: 341.29 MiB -> 341.17 MiB (-0.03%)