[PATCH] D37277: [TTI] Fix getGEPCost() for geps with a single operand

[Davide Italiano via Phabricator via llvm-commits]

davide created this revision.

Previously this would sporadically crash as `TargetType` was never initialized.
I just mimiced what the basic model does here, marking it as free. I'm happy to change this to Basic if folks think it's more appropriate.


https://reviews.llvm.org/D37277

Files:
  include/llvm/Analysis/TargetTransformInfoImpl.h
  test/Transforms/SimplifyCFG/gepcost.ll


Index: test/Transforms/SimplifyCFG/gepcost.ll
===================================================================
--- /dev/null
+++ test/Transforms/SimplifyCFG/gepcost.ll
@@ -0,0 +1,28 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -simplifycfg | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "thumbv7m-none--eabi"
+
+ at glob = external unnamed_addr constant [16 x i8]
+
+define void @f() {
+; CHECK-LABEL: @f(
+; CHECK-NEXT:  entr:
+; CHECK-NEXT:    br i1 undef, label [[NEXT:%.*]], label [[EXIT:%.*]]
+; CHECK:       next:
+; CHECK-NEXT:    [[PAT:%.*]] = getelementptr [16 x i8], [16 x i8]* @glob
+; CHECK-NEXT:    br label [[EXIT]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entr:
+  br i1 undef, label %next, label %exit
+
+next:
+  %pat = getelementptr [16 x i8], [16 x i8]* @glob
+  br label %exit
+
+exit:
+  ret void
+}
Index: include/llvm/Analysis/TargetTransformInfoImpl.h
===================================================================
--- include/llvm/Analysis/TargetTransformInfoImpl.h
+++ include/llvm/Analysis/TargetTransformInfoImpl.h
@@ -674,7 +674,7 @@
     int64_t Scale = 0;
 
     auto GTI = gep_type_begin(PointeeType, Operands);
-    Type *TargetType;
+    Type *TargetType = nullptr;
     for (auto I = Operands.begin(); I != Operands.end(); ++I, ++GTI) {
       TargetType = GTI.getIndexedType();
       // We assume that the cost of Scalar GEP with constant index and the
@@ -702,6 +702,10 @@
       }
     }
 
+    // If this GEP has a single operand, the basis, it should be cheap.
+    if (Operands.empty())
+      return TTI::TCC_Free;
+
     // Assumes the address space is 0 when Ptr is nullptr.
     unsigned AS =
         (Ptr == nullptr ? 0 : Ptr->getType()->getPointerAddressSpace());


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