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cd81639d2e
this code: store [stack slot #0], R10 = add R14, [stack slot #0] The spiller didn't know that the store made the value of [stackslot#0] available in R10 *IF* the store came from a copy instruction with the store folded into it. This patch teaches VirtRegMap to look at these stores and recognize the values they make available. In one case Evan provided, this code: divsd %XMM0, %XMM1 movsd %XMM1, QWORD PTR [%ESP + 40] 1) movsd QWORD PTR [%ESP + 48], %XMM1 2) movsd %XMM1, QWORD PTR [%ESP + 48] addsd %XMM1, %XMM0 3) movsd QWORD PTR [%ESP + 48], %XMM1 movsd QWORD PTR [%ESP + 4], %XMM0 turns into: divsd %XMM0, %XMM1 movsd %XMM1, QWORD PTR [%ESP + 40] addsd %XMM1, %XMM0 3) movsd QWORD PTR [%ESP + 48], %XMM1 movsd QWORD PTR [%ESP + 4], %XMM0 In this case, instruction #2 was removed because of the value made available by #1, and inst #1 was later deleted because it is now never used before the stack slot is redefined by #3. This occurs here and there in a lot of code with high spilling, on PPC most of the removed loads/stores are LSU-reject-causing loads, which is nice. On X86, things are much better (because it spills more), where we nuke about 1% of the instructions from SMG2000 and several hundred from eon. More improvements to come... git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25917 91177308-0d34-0410-b5e6-96231b3b80d8
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