[PATCH] D100383: [LSR] Fix for pre-indexed generated constant offset

[Stelios Ioannou via Phabricator via llvm-commits]

stelios-arm created this revision.
stelios-arm added reviewers: SjoerdMeijer, dmgreen, sanwou01, samparker, fhahn, NickGuy.
Herald added subscribers: arphaman, hiraditya.
stelios-arm requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Adds a check to ensure that  `LSRInstance::GenerateConstantOffsetsImpl`
generates an offset that results in a legal addressing mode and formula.

Currently when building a bootstrap build with the following flags:

  -DCMAKE_C_FLAGS="${CMAKE_C_FLAGS} -mllvm -lsr-preferred-addressing-mode=preindexed"  -DCMAKE_CXX_FLAGS="${CMAKE_C_FLAGS} -mllvm -lsr-preferred-addressing-mode=preindexed"

, it fails at compiling `TargetLoweringBase.cpp `because it generates an illegal formula.

This patch fixes this and allows to build a bootstrap build with the aforementioned flags.


https://reviews.llvm.org/D100383

Files:
  llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp


Index: llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -3833,7 +3833,13 @@
 
         for (int64_t Offset : Worklist) {
           Offset -= Step;
-          GenerateOffset(G, Offset);
+          Formula F = Base;
+          F.BaseOffset = (uint64_t)Base.BaseOffset - Offset;
+          // Check that the offset will result in a legal formula and addressing
+          // mode.
+          if (isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy,
+                         F))
+            GenerateOffset(G, Offset);
         }
       }
     }


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