[DebugInfo@O2] SimplifyCFG sink splitting drops a variable location

[jmorse]

Bugzilla Link	41881
Version	trunk
OS	Linux
Blocks	#38116
CC	@gregbedwell,@jdm,@OCHyams,@pogo59,@Melamoto

Extended Description

With llvm/clang r359863, running "clang -emit-llvm -O2 -g -S" on the code below, the dbg.value representing the assignment of "local = q" is dropped by SimplifyCFG. From the names of the basic blocks, it would appear to be the SinkCommonCodeFromPredecessors function that does the dropping.

--------8<--------
volatile int g, *x;

int baz(int p, int q) {
int local;

local = p;
switch (g) {
case 1:
x[1] = local;
g += p;
break;
case 2:
x[1] += p;
break;
case 3:
local = q;
g++;
break;
}

return 4 + q;
}
-------->8--------

In this particular test case the impact of dropping the "local=q" assignment is that the "local=p" assignment dominates all blocks, and an incorrect location for "local" is produce in the "case 3" and exit block. (Didn't test this as far as a debugger because I believe the error is fairly clear).