check_cfc: dash g generate different code with SelectionDAGISel

[llvmbot]

Bugzilla Link	44434
Version	trunk
OS	Linux
Blocks	#43767
Reporter	LLVM Bugzilla Contributor
CC	@topperc,@jmorse,@RKSimon,@pogo59,@rotateright

Extended Description

Based on the Bug 44422 - check_cfc: dash g generate different code with machine-cp. There is another issue that the "isel" pass make different output in the middle of the optimization, but the issue could not reproduce at the end, would this be ignored? or is an potential issue.

More analysis about this issue:

[Reproduce]
clang++ $HOME/test-suite/MultiSource/Benchmarks/Bullet/btConvexConvexAlgorithm.cpp -w -c -mllvm -opt-bisect-limit=669 -O2 -I $HOME/test-suite/MultiSource/Benchmarks/Bullet/include -o out1.o 2>log1
clang++ -g $HOME/test-suite/MultiSource/Benchmarks/Bullet/btConvexConvexAlgorithm.cpp -w -c -mllvm -opt-bisect-limit=699 -O2 -I $HOME/test-suite/MultiSource/Benchmarks/Bullet/include -o out2.o 2>log2
objdump -d -j .text out1.o > out1.obj
objdump -d -j .text out2.o > out2.obj
colordiff out1.obj out2.obj

[The case related with DAG Instruction Selection]

#Before X86 DAG->DAG Instruction Selection:
%60 = load float, float* %12, align 4, !dbg !​2196, !tbaa !​2011
call void @​llvm.dbg.value(metadata float %60, metadata !​2144, metadata !DIExpression()), !dbg !​2165
%61 = fsub float %59, %60

After X86 DAG->DAG Instruction Selection:

%29:fr32 = MOVSSrm_alt %stack.0, 1, $noreg, 0, $noreg, debug-location
DBG_VALUE %29:fr32, $noreg, !"capsuleRadiusB", !DIExpression()
%28:fr32 = SUBSSrr killed %31:fr32(tied-def 0), killed %29:fr32, implicit $mxcsr

Expectation:

%28:fr32 = SUBSSrm killed %30:fr32(tied-def 0), %stack.0, 1, $noreg, 0, $noreg, implicit $mxcsr :: (load 4 from %ir.12, !tbaa !​46)

---

In the file lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp,
and the function SelectAllBasicBlock(),
while try to select the instruction with FastISel,
FastIS>tryToFoldLoad() is not implemented because of the dbg_value which block "fold the load", break by (!isFoldedOrDeadInstruction()).