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Before: adr r12, #LJTI3_0_0 ldr pc, [r12, +r0, lsl #2] LJTI3_0_0: .long LBB3_24 .long LBB3_30 .long LBB3_31 .long LBB3_32 After: adr r12, #LJTI3_0_0 add pc, r12, +r0, lsl #2 LJTI3_0_0: b.w LBB3_24 b.w LBB3_30 b.w LBB3_31 b.w LBB3_32 This has several advantages. 1. This will make it easier to optimize this to a TBB / TBH instruction + (smaller) table. 2. This eliminate the need for ugly asm printer hack to force the address into thumb addresses (bit 0 is one). 3. Same codegen for pic and non-pic. 4. This eliminate the need to align the table so constantpool island pass won't have to over-estimate the size. Based on my calculation, the later is probably slightly faster as well since ldr pc with shifter address is very slow. That is, it should be a win as long as the HW implementation can do a reasonable job of branch predict the second branch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77024 91177308-0d34-0410-b5e6-96231b3b80d8
12 lines
579 B
Plaintext
12 lines
579 B
Plaintext
//===---------------------------------------------------------------------===//
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// Random ideas for the ARM backend (Thumb2 specific).
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//===---------------------------------------------------------------------===//
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* We should model IT instructions explicitly. We should introduce them (even if
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if-converter is not run, the function could still contain movcc's) before
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PEI since passes starting from PEI may require exact code size.
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//===---------------------------------------------------------------------===//
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Make use of TBB and TBH for jumptables in small functions.
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