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[CodeGen] Increase the size of a SmallVector
The SmallVector reserve() call in MachineInstrExpressionTrait::getHashValue accounted for over 3% of all calls to malloc() when I compiled a bunch of graphics shaders for the AMDGPU target. Its initial size was only enough for machine instructions with up to 7 operands, but for AMDGPU 8 and 10 operands are very common. Here's a histogram of number of operands for each call to getHashValue, gathered from the same collection of shaders: 1 13503 2 254273 3 135781 4 422508 5 614997 6 194953 7 287248 8 1517255 9 31218 10 1191269 11 70731 12 24 13 77 15 84 17 4692 27 16 33 705 49 6 Typical instructions with 8 and 10 operands are floating point arithmetic and multiply-accumulate instructions like: %83:vgpr_32 = V_MUL_F32_e64 0, killed %82:vgpr_32, 0, killed %81:vgpr_32, 0, 0, implicit $exec %330:vgpr_32 = V_MAC_F32_e64 0, killed %327:vgpr_32, 0, killed %329:sgpr_32, 0, %328:vgpr_32(tied-def 0), 0, 0, implicit $exec Differential Revision: https://reviews.llvm.org/D70301
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