[RS4GC] Avoid crashing on gep scalar_base, vector_idx
This is an alternative to https://reviews.llvm.org/D57103. After discussion, we dedicided to check this in as a temporary workaround, and pursue a true fix under the original thread.
The issue at hand is that the base rewriting algorithm doesn't consider the fact that GEPs can turn a scalar input into a vector of outputs. We had handling for scalar GEPs and fully vector GEPs (i.e. all vector operands), but not the scalar-base + vector-index forms. A true fix here requires treating GEP analogously to extractelement or shufflevector.
This patch is merely a workaround. It simply hides the crash at the cost of some ugly code gen for this presumable very rare pattern.
Differential Revision: https://reviews.llvm.org/D57138
llvm-svn: 352059
diff --git a/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp b/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
index 81dd4b5..e722456 100644
--- a/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
+++ b/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
@@ -2601,6 +2601,34 @@
}
}
+ // Nasty workaround - The base computation code in the main algorithm doesn't
+ // consider the fact that a GEP can be used to convert a scalar to a vector.
+ // The right fix for this is to integrate GEPs into the base rewriting
+ // algorithm properly, this is just a short term workaround to prevent
+ // crashes by canonicalizing such GEPs into fully vector GEPs.
+ for (Instruction &I : instructions(F)) {
+ if (!isa<GetElementPtrInst>(I))
+ continue;
+
+ unsigned VF = 0;
+ bool HasScalarOperand = false;
+ for (unsigned i = 0; i < I.getNumOperands(); i++)
+ if (I.getOperand(i)->getType()->isVectorTy())
+ VF = I.getOperand(i)->getType()->getVectorNumElements();
+ else
+ HasScalarOperand = true;
+
+ if (HasScalarOperand && VF != 0) {
+ IRBuilder<> B(&I);
+ for (unsigned i = 0; i < I.getNumOperands(); i++)
+ if (!I.getOperand(i)->getType()->isVectorTy()) {
+ auto *Splat = B.CreateVectorSplat(VF, I.getOperand(i));
+ I.setOperand(i, Splat);
+ MadeChange = true;
+ }
+ }
+ }
+
MadeChange |= insertParsePoints(F, DT, TTI, ParsePointNeeded);
return MadeChange;
}