[PATCH] D55169: [ConstantFolding] Handle leading zero-length elements in load folding

[Nikita Popov via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL348895: [ConstantFolding] Handle leading zero-size elements in load folding (authored by nikic, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D55169?vs=177675&id=177758#toc

Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D55169/new/

https://reviews.llvm.org/D55169

Files:
  llvm/trunk/lib/Analysis/ConstantFolding.cpp
  llvm/trunk/test/Transforms/ConstProp/loads.ll


Index: llvm/trunk/test/Transforms/ConstProp/loads.ll
===================================================================
--- llvm/trunk/test/Transforms/ConstProp/loads.ll
+++ llvm/trunk/test/Transforms/ConstProp/loads.ll
@@ -269,3 +269,42 @@
 ; BE-LABEL: @test16.3(
 ; BE: ret i64 0
 }
+
+ at g7 = constant {[0 x i32], [0 x i8], {}*} { [0 x i32] undef, [0 x i8] undef, {}* null }
+
+define i64* @test_leading_zero_size_elems() {
+  %v = load i64*, i64** bitcast ({[0 x i32], [0 x i8], {}*}* @g7 to i64**)
+  ret i64* %v
+
+; LE-LABEL: @test_leading_zero_size_elems(
+; LE: ret i64* null
+
+; BE-LABEL: @test_leading_zero_size_elems(
+; BE: ret i64* null
+}
+
+ at g8 = constant {[4294967295 x [0 x i32]], i64} { [4294967295 x [0 x i32]] undef, i64 123 }
+
+define i64 @test_leading_zero_size_elems_big() {
+  %v = load i64, i64* bitcast ({[4294967295 x [0 x i32]], i64}* @g8 to i64*)
+  ret i64 %v
+
+; LE-LABEL: @test_leading_zero_size_elems_big(
+; LE: ret i64 123
+
+; BE-LABEL: @test_leading_zero_size_elems_big(
+; BE: ret i64 123
+}
+
+ at g9 = constant [4294967295 x [0 x i32]] zeroinitializer
+
+define i64 @test_array_of_zero_size_array() {
+  %v = load i64, i64* bitcast ([4294967295 x [0 x i32]]* @g9 to i64*)
+  ret i64 %v
+
+; LE-LABEL: @test_array_of_zero_size_array(
+; LE: ret i64 0
+
+; BE-LABEL: @test_array_of_zero_size_array(
+; BE: ret i64 0
+}
Index: llvm/trunk/lib/Analysis/ConstantFolding.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ConstantFolding.cpp
+++ llvm/trunk/lib/Analysis/ConstantFolding.cpp
@@ -347,9 +347,20 @@
 
     // We're simulating a load through a pointer that was bitcast to point to
     // a different type, so we can try to walk down through the initial
-    // elements of an aggregate to see if some part of th e aggregate is
+    // elements of an aggregate to see if some part of the aggregate is
     // castable to implement the "load" semantic model.
-    C = C->getAggregateElement(0u);
+    if (SrcTy->isStructTy()) {
+      // Struct types might have leading zero-length elements like [0 x i32],
+      // which are certainly not what we are looking for, so skip them.
+      unsigned Elem = 0;
+      Constant *ElemC;
+      do {
+        ElemC = C->getAggregateElement(Elem++);
+      } while (ElemC && DL.getTypeSizeInBits(ElemC->getType()) == 0);
+      C = ElemC;
+    } else {
+      C = C->getAggregateElement(0u);
+    }
   } while (C);
 
   return nullptr;


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