From d9ec3572f3d0997348361334446f942194522127 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Sat, 8 Jan 2011 08:24:46 +0000 Subject: [PATCH] Have loop-rotate simplify instructions (yay instsimplify!) as it clones 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 --- lib/Transforms/Scalar/LoopRotation.cpp | 26 +++++++++++++++++---- test/Transforms/LoopRotate/phi-duplicate.ll | 5 ++-- 2 files changed, 23 insertions(+), 8 deletions(-) diff --git a/lib/Transforms/Scalar/LoopRotation.cpp b/lib/Transforms/Scalar/LoopRotation.cpp index 4ca422e6209..2b00caeb4e0 100644 --- a/lib/Transforms/Scalar/LoopRotation.cpp +++ b/lib/Transforms/Scalar/LoopRotation.cpp @@ -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 diff --git a/test/Transforms/LoopRotate/phi-duplicate.ll b/test/Transforms/LoopRotate/phi-duplicate.ll index 5403e723ee1..c252a32d515 100644 --- a/test/Transforms/LoopRotate/phi-duplicate.ll +++ b/test/Transforms/LoopRotate/phi-duplicate.ll @@ -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: } -- 2.34.1