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Have loop-rotate simplify instructions (yay instsimplify!) as it clones

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them into the loop preheader, eliminating silly instructions like
"icmp i32 0, 100" in fixed tripcount loops.  This also better exposes the 
bigger problem with loop rotate that I'd like to fix: once this has been
folded, the duplicated conditional branch *often* turns into an uncond branch.

Not aggressively handling this is pessimizing later loop optimizations 
somethin' fierce by making "dominates all exit blocks" checks fail.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123060 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2011-01-08 08:24:46 +00:00
parent c3942eb95d
commit d9ec3572f3
2 changed files with 23 additions and 8 deletions
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26
lib/Transforms/Scalar/LoopRotation.cpp
View File

@ -14,9 +14,10 @@
#define DEBUG_TYPE "loop-rotate"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Function.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/DominanceFrontier.h"
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/DominanceFrontier.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
@ -205,9 +206,24 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {
// Otherwise, create a duplicate of the instruction.
Instruction *C = Inst->clone();
C->setName(Inst->getName());
C->insertBefore(LoopEntryBranch);
ValueMap[Inst] = C;
// Eagerly remap the operands of the instruction.
RemapInstruction(C, ValueMap,
RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
// With the operands remapped, see if the instruction constant folds or is
// otherwise simplifyable. This commonly occurs because the entry from PHI
// nodes allows icmps and other instructions to fold.
if (Value *V = SimplifyInstruction(C)) {
// If so, then delete the temporary instruction and stick the folded value
// in the map.
delete C;
ValueMap[Inst] = V;
} else {
// Otherwise, stick the new instruction into the new block!
C->setName(Inst->getName());
C->insertBefore(LoopEntryBranch);
ValueMap[Inst] = C;
}
}
// Along with all the other instructions, we just cloned OrigHeader's

5
test/Transforms/LoopRotate/phi-duplicate.ll
View File

@ -34,14 +34,13 @@ for.end: ; preds = %for.cond
; CHECK: define void @test
; CHECK-NEXT: entry:
; CHECK-NEXT: icmp slt i64
; CHECK-NEXT: br i1
; CHECK-NEXT: br i1 true, label %bb.nph, label %for.end
; CHECK-NOT: :
; CHECK: bb.nph:
; CHECK-NEXT: br label %for.body
; CHECK-NOT: :
; CHECK: for.body:
; CHECK-NEXT: %j.02 = phi i64
; CHECK-NEXT: %j.01 = phi i64
; CHECK-NOT: phi
; CHECK: ret void
; CHECK-NEXT: }