[RS4GC] Be slightly less conservative for gep vector_base, scalar_idx

[reames]

Summary

After submitting https://reviews.llvm.org/D57138, I realized it was slightly more conservative than needed. The scalar indices don't appear to be a problem on a scalar gep, we even had a test for that.

[anna]

The scalar indices don't appear to be a problem on a scalar gep, we even had a test for that.

just to note it is not a scalar gep - this is a vector gep which has a scalar index.

[anna]

lgtm.

lib/Transforms/Scalar/RewriteStatepointsForGC.cpp

bool RewriteStatepointsForGC::runOnFunction(Function &F, DominatorTree &DT,
   // 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())
+      if (I.getOperand(i)->getType()->isVectorTy()) {
+        assert(VF == 0 ||
+               VF == I.getOperand(i)->getType()->getVectorNumElements());
         VF = I.getOperand(i)->getType()->getVectorNumElements();
-      else
-        HasScalarOperand = true;
+      }
 
-    if (HasScalarOperand && VF != 0) {
+    // It's the vector to scalar traversal through the pointer operand which
+    // confuses base pointer rewriting, so limit ourselves to that case.
+    if (!I.getOperand(0)->getType()->isVectorTy() && 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;
-        }
-    }
-  }
+      auto *Splat = B.CreateVectorSplat(VF, I.getOperand(0));
+      I.setOperand(0, Splat);
 
   MadeChange |= insertParsePoints(F, DT, TTI, ParsePointNeeded);
   return MadeChange;
 }
 
 // liveness computation via standard dataflow
 // -------------------------------------------------------------------
 

test/Transforms/RewriteStatepointsForGC/base-vector.ll

 }
 declare void @do_safepoint()
 
 define void @test11(<4 x i64 addrspace(1)*> %vec1) gc "statepoint-example" {
 ; CHECK-LABEL: @test11(
 ; CHECK: @llvm.experimental.gc.statepoint.p0f_isVoidf{{.*}}<4 x i64 addrspace(1)*> %vec1)
 ; CHECK: %vec1.relocated = call coldcc <4 x i8 addrspace(1)*> @llvm.experimental.gc.relocate.v4p1i8
 ; CHECK: %vec1.relocated.casted = bitcast <4 x i8 addrspace(1)*> %vec1.relocated to <4 x i64 addrspace(1)*>
-; CHECK: %vec2.remat = getelementptr i64, <4 x i64 addrspace(1)*> %vec1.relocated.casted, <4 x i32> <i32 1024, i32 1024, i32 1024, i32 1024>
+; CHECK: %vec2.remat = getelementptr i64, <4 x i64 addrspace(1)*> %vec1.relocated.casted, i32 1024
 ; CHECK: call void @use_vec(<4 x i64 addrspace(1)*> %vec2.remat)
 entry:
   %vec2 = getelementptr i64, <4 x i64 addrspace(1)*> %vec1, i32 1024
   call void @do_safepoint() [ "deopt"(i32 0, i32 -1, i32 0, i32 0, i32 0) ]
   call void @use_vec(<4 x i64 addrspace(1) *> %vec2)
   ret void
 }