[InlineCost] GetElementPtr with constant operands

If the GEP instruction contanins only constants as its arguments,
then it should be recognized as a constant. For now, there was
also added a flag to turn off this simplification if it causes
any regressions ("disable-gep-const-evaluation") which is off
by default. Once I gather needed data of the effectiveness of
this simplification, the flag will be deleted.

Reviewers: apilipenko, davidxl, mtrofin

Reviewed By: mtrofin

Differential Revision: https://reviews.llvm.org/D81026

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/InlineCost.cpp b/llvm/lib/Analysis/InlineCost.cpp
index c05d1ee7..33d7144 100644
--- a/llvm/lib/Analysis/InlineCost.cpp
+++ b/llvm/lib/Analysis/InlineCost.cpp
@@ -110,6 +110,10 @@ static cl::opt<bool> InlineCallerSupersetNoBuiltin(
     cl::desc("Allow inlining when caller has a superset of callee's nobuiltin "
              "attributes."));
 
+static cl::opt<bool> DisableGEPConstOperand(
+    "disable-gep-const-evaluation", cl::Hidden, cl::init(false),
+    cl::desc("Disables evaluation of GetElementPtr with constant operands"));
+
 namespace {
 class InlineCostCallAnalyzer;
 
@@ -1019,6 +1023,16 @@ bool CallAnalyzer::visitGetElementPtr(GetElementPtrInst &I) {
     return true;
   };
 
+  if (!DisableGEPConstOperand)
+    if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
+        SmallVector<Constant *, 2> Indices;
+        for (unsigned int Index = 1 ; Index < COps.size() ; ++Index)
+            Indices.push_back(COps[Index]);
+        return ConstantExpr::getGetElementPtr(I.getSourceElementType(), COps[0],
+                                              Indices, I.isInBounds());
+        }))
+      return true;
+
   if ((I.isInBounds() && canFoldInboundsGEP(I)) || IsGEPOffsetConstant(I)) {
     if (SROAArg)
       SROAArgValues[&I] = SROAArg;