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Improve branch folding by recgonizing that explict successor relationships impact the value of fall-through choices.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44785 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Christopher Lamb 2007-12-10 07:24:06 +00:00
parent 53c34b1db9
commit 11a4f64bd4
2 changed files with 6 additions and 3 deletions
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5
lib/CodeGen/BranchFolding.cpp
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@ -775,6 +775,11 @@ static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
// optimize branches that branch to either a return block or an assert block
// into a fallthrough to the return.
if (MBB1->empty() || MBB2->empty()) return false;
// If there is a clear successor ordering we make sure that one block
// will fall through to the next
if (MBB1->isSuccessor(MBB2)) return true;
if (MBB2->isSuccessor(MBB1)) return false;
MachineInstr *MBB1I = --MBB1->end();
MachineInstr *MBB2I = --MBB2->end();

4
test/CodeGen/X86/2007-06-14-branchfold.ll
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@ -1,7 +1,5 @@
; RUN: llvm-as < %s | llc -mcpu=i686 | grep jmp | count 1
; RUN: llvm-as < %s | llc -mcpu=i686 | not grep jmp
; check that branch folding understands FP_REG_KILL is not a branch
; the remaining jmp can be removed if we take advantage of knowing
; abort does not return
; ModuleID = 'g.bc'
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64"