[PATCH] Allow isDereferencablePointer to look through BitCast ConstantExprs

[Michael Kuperstein]

Hi hfinkel,

isDereferencablePointer looks through BitCast instructions, but not constant expressions.
This fixes PR22460.

I could have both sides of the if use the same code - but it would have to be the one for the ConstantExpr side. 
Is that better?

http://reviews.llvm.org/D7411

Files:
  lib/IR/Value.cpp
  test/Transforms/LICM/constexpr.ll

Index: lib/IR/Value.cpp
===================================================================
--- lib/IR/Value.cpp
+++ lib/IR/Value.cpp
@@ -495,17 +495,29 @@
   // to a type of smaller size (or the same size), and the alignment
   // 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)) {
-      Type *STy = BC->getSrcTy()->getPointerElementType(),
-           *DTy = BC->getDestTy()->getPointerElementType();
-      if (STy->isSized() && DTy->isSized() &&
+  if (DL) {
+    Type *STy = nullptr, *DTy = nullptr;
+    Value *SrcVal = nullptr;
+    
+    if (const BitCastInst *BC = dyn_cast<BitCastInst>(V)) {
+      SrcVal = BC->getOperand(0);
+      STy = BC->getSrcTy()->getPointerElementType();
+      DTy = BC->getDestTy()->getPointerElementType();
+    } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
+      if (CE->getOpcode() == Instruction::BitCast) {
+        SrcVal = CE->getOperand(0);
+        STy = SrcVal->getType()->getPointerElementType();
+        DTy = CE->getType()->getPointerElementType();
+      }
+    }
+
+    if (STy && STy->isSized() && DTy->isSized() &&
           (DL->getTypeStoreSize(STy) >=
            DL->getTypeStoreSize(DTy)) &&
           (DL->getABITypeAlignment(STy) >=
            DL->getABITypeAlignment(DTy)))
-        return isDereferenceablePointer(BC->getOperand(0), DL, Visited);
-    }
+      return isDereferenceablePointer(SrcVal, DL, Visited);
+  }
 
   // Global variables which can't collapse to null are ok.
   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
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
+}

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D7411.19321.patch
Type: text/x-patch
Size: 3456 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20150204/ed948356/attachment.bin>