[llvm] a7322a2 - [LICM] Delay fetching of preheader (NFC)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-03-10T16:16:48+01:00
New Revision: a7322a2171e99fe9c465c3e13c49563b19402ae0

URL: https://github.com/llvm/llvm-project/commit/a7322a2171e99fe9c465c3e13c49563b19402ae0
DIFF: https://github.com/llvm/llvm-project/commit/a7322a2171e99fe9c465c3e13c49563b19402ae0.diff

LOG: [LICM] Delay fetching of preheader (NFC)

Only fetch preheader once we want to actually hoist. It turns out
that calculating the preheader is expensive enough to affect
overall compile-time if you do it for every single instruction.

Addresses the compile-time regression from D143726.

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/LICM.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index a79e3955ce18..b181fae22f26 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -2415,8 +2415,6 @@ bool pointerInvalidatedByBlock(BasicBlock &BB, MemorySSA &MSSA, MemoryUse &MU) {
 
 static bool hoistMinMax(Instruction &I, Loop &L, ICFLoopSafetyInfo &SafetyInfo,
                         MemorySSAUpdater &MSSAU) {
-  auto *Preheader = L.getLoopPreheader();
-  assert(Preheader && "Loop is not in simplify form?");
   bool Inverse = false;
   bool IsLogical = false;
   using namespace PatternMatch;
@@ -2465,6 +2463,8 @@ static bool hoistMinMax(Instruction &I, Loop &L, ICFLoopSafetyInfo &SafetyInfo,
   Intrinsic::ID id = ICmpInst::isSigned(P1)
                          ? (UseMin ? Intrinsic::smin : Intrinsic::smax)
                          : (UseMin ? Intrinsic::umin : Intrinsic::umax);
+  auto *Preheader = L.getLoopPreheader();
+  assert(Preheader && "Loop is not in simplify form?");
   IRBuilder<> Builder(Preheader->getTerminator());
   // We are about to create a new guaranteed use for RHS2 which might not exist
   // before (if it was a non-taken input of logical and/or instruction). If it