[PATCH] D13532: [CGP] widen switch condition and case constants to target's register width

[Sanjay Patel via llvm-commits]

spatel created this revision.
spatel added reviewers: hfinkel, reames, joker.eph.
spatel added a subscriber: llvm-commits.

This is a follow-up from the discussion in D12965. The block-at-a-time limitation of SelectionDAG also came up in D13297.

Without the InstCombine change from D12965, I don't expect this patch to make any difference in the real world because InstCombine will already be widening cases like this in visitSwitchInst(). But we need to have this CGP safety harness in place before proceeding with any shrinkage in D12965, so we won't generate extra extends for compares.

There are regression tests for CGP in both test/Transforms/CodeGenPrepare and test/CodeGen/* . I opted for IR regression tests in the patch because that seems like a clearer way to test the transform, but PowerPC CodeGen for the i16 widening test is shown below. x86 will need more work to solve: https://llvm.org/bugs/show_bug.cgi?id=22473

Before:
  # BB#0:      
    mr 4, 3
    extsh. 3, 4
    ble 0, .LBB0_5
  # BB#1:              
    cmpwi	 3, 99
    bgt	 0, .LBB0_9
  # BB#2:            
    rlwinm 4, 4, 0, 16, 31      <--- 32-bit mask/extend
    li 3, 0
    cmplwi	 4, 1
    beqlr 0
  # BB#3:            
    cmplwi	 4, 10
    bne	 0, .LBB0_12
  # BB#4:                      
    li 3, 1
    blr
  .LBB0_5:                             
    rlwinm 3, 4, 0, 16, 31         <--- 32-bit mask/extend
    cmplwi	 3, 65436
    beq	 0, .LBB0_13
  # BB#6:                            
    cmplwi	 3, 65526
    beq	 0, .LBB0_15
  # BB#7:                       
    cmplwi	 3, 65535
    bne	 0, .LBB0_12
  # BB#8:                       
    li 3, 4
    blr
  .LBB0_9:                       
    rlwinm 3, 4, 0, 16, 31      <--- 32-bit mask/extend
    cmplwi	 3, 100
    beq	 0, .LBB0_14
  ...

After:
  # BB#0:        
    rlwinm 4, 3, 0, 16, 31   <--- mask/extend to 32-bit and then use that for comparisons
    cmpwi	 4, 999
    ble 0, .LBB0_5
  # BB#1:          
    lis 3, 0
    ori 3, 3, 65525
    cmpw	 4, 3
    bgt	 0, .LBB0_9
  # BB#2:         
    cmplwi	 4, 1000
    beq	 0, .LBB0_14
 # BB#3:    
    cmplwi	 4, 65436
    bne	 0, .LBB0_13
  # BB#4:       
    li 3, 6
    blr
  .LBB0_5:   
    li 3, 0
    cmplwi	 4, 1
    beqlr 0
  # BB#6: 
    cmplwi	 4, 10
    beq	 0, .LBB0_12
  # BB#7:             
    cmplwi	 4, 100
    bne	 0, .LBB0_13
  # BB#8:             
    li 3, 2
    blr
  .LBB0_9:       
    cmplwi	 4, 65526
    beq	 0, .LBB0_15
  # BB#10:      
    cmplwi	 4, 65535
    bne	 0, .LBB0_13
  ...


http://reviews.llvm.org/D13532

Files:
  lib/CodeGen/CodeGenPrepare.cpp
  test/Transforms/CodeGenPrepare/widen_switch.ll

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