[PATCH] Allow isDereferencablePointer to look through BitCast ConstantExprs

[Michael Kuperstein]

Thanks Hal, David!
David, your suggestion almost works. What do you think about this?


http://reviews.llvm.org/D7411

Files:
  include/llvm/IR/Operator.h
  lib/IR/Value.cpp
  test/Transforms/LICM/constexpr.ll

Index: test/Transforms/LICM/constexpr.ll
===================================================================
--- test/Transforms/LICM/constexpr.ll
+++ test/Transforms/LICM/constexpr.ll
@@ -0,0 +1,46 @@
+; RUN: opt < %s -S -basicaa -licm | FileCheck %s
+; This fixes PR22460
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+ at in = internal unnamed_addr global i32* null, align 8
+ at out = internal unnamed_addr global i32* null, align 8
+
+; CHECK-LABEL: @bar
+; CHECK: entry:
+; CHECK: load i64* bitcast (i32** @in to i64*)
+; CHECK: do.body:
+; CHECK-NOT: load
+
+define i64 @bar(i32 %N) {
+entry:
+  br label %do.body
+
+do.body:                                          ; preds = %l2, %entry
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %l2 ]
+  %total = phi i64 [ 0, %entry ], [ %next, %l2 ]
+  %c = icmp eq i32 %N, 6
+  br i1 %c, label %l1, label %do.body.l2_crit_edge
+
+do.body.l2_crit_edge:                             ; preds = %do.body
+  %inval.pre = load i32** @in, align 8
+  br label %l2
+
+l1:                                               ; preds = %do.body
+  %v1 = load i64* bitcast (i32** @in to i64*), align 8
+  store i64 %v1, i64* bitcast (i32** @out to i64*), align 8
+  %0 = inttoptr i64 %v1 to i32*
+  br label %l2
+
+l2:                                               ; preds = %do.body.l2_crit_edge, %l1
+  %inval = phi i32* [ %inval.pre, %do.body.l2_crit_edge ], [ %0, %l1 ]
+  %int = ptrtoint i32* %inval to i64
+  %next = add i64 %total, %int
+  %inc = add nsw i32 %i.0, 1
+  %cmp = icmp slt i32 %inc, %N
+  br i1 %cmp, label %do.body, label %do.end
+
+do.end:                                           ; preds = %l2
+  ret i64 %total
+}
Index: include/llvm/IR/Operator.h
===================================================================
--- include/llvm/IR/Operator.h
+++ include/llvm/IR/Operator.h
@@ -504,6 +504,20 @@
   }
 };
 
+class BitCastOperator
+    : public ConcreteOperator<Operator, Instruction::BitCast> {
+  friend class BitCastInst;
+  friend class ConstantExpr;
+
+public:
+  Type *getSrcTy() const {
+    return getOperand(0)->getType();
+  }
+
+  Type *getDestTy() const {
+    return getType();
+  }
+};
 
 } // End llvm namespace
 
Index: lib/IR/Value.cpp
===================================================================
--- lib/IR/Value.cpp
+++ lib/IR/Value.cpp
@@ -496,7 +496,7 @@
   // is at least as large as for the resulting pointer type, then
   // we can look through the bitcast.
   if (DL)
-    if (const BitCastInst* BC = dyn_cast<BitCastInst>(V)) {
+    if (const BitCastOperator *BC = dyn_cast<BitCastOperator>(V)) {
       Type *STy = BC->getSrcTy()->getPointerElementType(),
            *DTy = BC->getDestTy()->getPointerElementType();
       if (STy->isSized() && DTy->isSized() &&

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