[PATCH] D36772: Unmerge GEPs to reduce register pressure on IndirectBr edges.

[Hal Finkel via Phabricator via llvm-commits]

hfinkel added a comment.

This is looking good. A couple additional things...



================
Comment at: lib/CodeGen/CodeGenPrepare.cpp:6224
+    // that SrcBlock is the only precedessor of it. If not, give up.
+    if (UI->getParent()->getSinglePredecessor() != SrcBlock)
+      return false;
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I don't think this check is necessary. GEPIOp is constrained to be defined in SrcBlock, and it's SrcBlock that has the IndirectBr terminator, so *any* use of GEPIOp outside of SrcBlock keeps it live over the indirect edge. I don't see why we wouldn't unmerge regardless of the parent block here.


================
Comment at: lib/CodeGen/CodeGenPrepare.cpp:6264
+    UGEPI->setOperand(1, NewUGEPIIdx);
+  }
+  // After unmerging, verify that GEPIOp is actually only used in SrcBlock (not
----------------
You'll also need to make sure that this GEP is not marked as inbounds if GEPI was not.

  if (!GEPI->isInBounds()) {
    UGEPI->setIsInBounds(false);
  }

because otherwise the result of GEP could be not-in-bounds resulting in UB if that's used as the input to an inbounds UGEPI.


https://reviews.llvm.org/D36772