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d320dddb9e
Summary:
For inalloca functions, this is a very common code pattern:
%argpack = type <{ i32, i32, i32 }>
define void @f(%argpack* inalloca %args) {
entry:
%a = getelementptr inbounds %argpack, %argpack* %args, i32 0, i32 0
%b = getelementptr inbounds %argpack, %argpack* %args, i32 0, i32 1
%c = getelementptr inbounds %argpack, %argpack* %args, i32 0, i32 2
tail call void @llvm.dbg.declare(metadata i32* %a, ... "a")
tail call void @llvm.dbg.declare(metadata i32* %c, ... "b")
tail call void @llvm.dbg.declare(metadata i32* %b, ... "c")
Even though these GEPs can be simplified to a constant offset from EBP
or RSP, we don't do that at -O0, and each GEP is computed into a
register. Registers used to compute argument addresses are typically
spilled and clobbered very quickly after the initial computation, so
live debug variable tracking loses information very quickly if we use
DBG_VALUE instructions.
This change moves processing of dbg.declare between argument lowering
and basic block isel, so that we can ask if an argument has a frame
index or not. If the argument lives in a register as is the case for
byval arguments on some targets, then we don't put it in the side table
and during ISel we emit DBG_VALUE instructions.
Reviewers: aprantl
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D32980
llvm-svn: 302483
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