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Revert the main portion of r31856. It was causing BranchFolding

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to break up CFG diamonds by banishing one of the blocks to the end of
the function, which is bad for code density and branch size.

This does pessimize MultiSource/Benchmarks/Ptrdist/yacr2, the
benchmark cited as the reason for the change, however I've examined
the code and it looks more like a case of gaming a particular
branch than of being generally applicable.

llvm-svn: 84803
This commit is contained in:
Dan Gohman 2009-10-22 00:03:58 +00:00
parent f9d56f4830
commit 2d8e5654a8
4 changed files with 14 additions and 14 deletions
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10
lib/CodeGen/BranchFolding.cpp
View File

@ -945,15 +945,15 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
}
}
// If this block doesn't fall through (e.g. it ends with an uncond branch or
// has no successors) and if the pred falls through into this block, and if
// it would otherwise fall through into the block after this, move this
// block to the end of the function.
// If this block has no successors (e.g. it is a return block or ends with
// a call to a no-return function like abort or __cxa_throw) and if the pred
// falls through into this block, and if it would otherwise fall through
// into the block after this, move this block to the end of the function.
//
// We consider it more likely that execution will stay in the function (e.g.
// due to loops) than it is to exit it. This asserts in loops etc, moving
// the assert condition out of the loop body.
if (!PriorCond.empty() && PriorFBB == 0 &&
if (MBB->succ_empty() && !PriorCond.empty() && PriorFBB == 0 &&
MachineFunction::iterator(PriorTBB) == FallThrough &&
!CanFallThrough(MBB)) {
bool DoTransform = true;

2
test/CodeGen/CellSPU/2009-01-01-BrCond.ll
View File

@ -1,4 +1,4 @@
; RUN: llc < %s -march=cellspu -o - | grep brz
; RUN: llc < %s -march=cellspu -o - | grep brnz
; PR3274
target datalayout = "E-p:32:32:128-i1:8:128-i8:8:128-i16:16:128-i32:32:128-i64:32:128-f32:32:128-f64:64:128-v64:64:64-v128:128:128-a0:0:128-s0:128:128"

4
test/CodeGen/Generic/switch-lower-feature-2.ll
View File

@ -5,9 +5,9 @@
; RUN: grep 1023 %t | count 1
; RUN: grep 119 %t | count 1
; RUN: grep JTI %t | count 2
; RUN: grep jg %t | count 1
; RUN: grep jg %t | count 3
; RUN: grep ja %t | count 1
; RUN: grep js %t | count 1
; RUN: grep jns %t | count 1
target triple = "i686-pc-linux-gnu"

12
test/CodeGen/X86/loop-blocks.ll
View File

@ -74,16 +74,16 @@ exit:
; CHECK: yet_more_involved:
; CHECK: jmp .LBB3_1
; CHECK-NEXT: align
; CHECK-NEXT: .LBB3_7:
; CHECK-NEXT: call block_a_true_func
; CHECK-NEXT: jmp .LBB3_4
; CHECK-NEXT: .LBB3_2:
; CHECK-NEXT: .LBB3_3:
; CHECK-NEXT: call bar99
; CHECK-NEXT: call get
; CHECK-NEXT: cmpl $2999, %eax
; CHECK-NEXT: jle .LBB3_7
; CHECK-NEXT: jg .LBB3_5
; CHECK-NEXT: call block_a_true_func
; CHECK-NEXT: jmp .LBB3_6
; CHECK-NEXT: .LBB3_5:
; CHECK-NEXT: call block_a_false_func
; CHECK-NEXT: .LBB3_4:
; CHECK-NEXT: .LBB3_6:
; CHECK-NEXT: call block_a_merge_func
; CHECK-NEXT: .LBB3_1:
; CHECK-NEXT: call body