Change the way the lint sanity checking pass detects misaligned memory accesses.

Previously it was only be able to detect problems if the pointer was a numerical
value (eg inttoptr i32 1 to i32*), but not if it was an alloca or globa.  The
reason was the use of ComputeMaskedBits: imagine you have "alloca i8, align 2",
and ask ComputeMaskedBits what it knows about the bits of the alloca pointer.
It can tell you that the bottom bit is known zero (due to align 2) but it can't
tell you that bit 1 is known one.  That's because the address could be an even
multiple of 2 rather than an odd multiple, eg it might be a multiple of 4.  Thus
trying to use KnownOne is ineffective in the case of an alloca as it will never
have any bits set.  Instead look explicitly for constant offsets from allocas
and globals.

llvm-svn: 164595

diff --git a/llvm/lib/Analysis/Lint.cpp b/llvm/lib/Analysis/Lint.cpp
index 83bdf5286ad7deab58b6f728de82d384563fa02d..6e765a7fdea405c360800d528060263dceaf3d4b 100644 (file)
--- a/llvm/lib/Analysis/Lint.cpp
+++ b/llvm/lib/Analysis/Lint.cpp
@@ -412,14 +412,26 @@ void Lint::visitMemoryReference(Instruction &I,
   }
 
   if (TD) {
-    if (Align == 0 && Ty) Align = TD->getABITypeAlignment(Ty);
+    if (Align == 0 && Ty && Ty->isSized())
+      Align = TD->getABITypeAlignment(Ty);
 
     if (Align != 0) {
-      unsigned BitWidth = TD->getTypeSizeInBits(Ptr->getType());
-      APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-      ComputeMaskedBits(Ptr, KnownZero, KnownOne, TD);
-      Assert1(!(KnownOne & APInt::getLowBitsSet(BitWidth, Log2_32(Align))),
-              "Undefined behavior: Memory reference address is misaligned", &I);
+      int64_t Offset = 0;
+      if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *TD)) {
+        unsigned BaseAlign = 0;
+        if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
+          BaseAlign = AI->getAlignment();
+          if (BaseAlign == 0 && AI->getAllocatedType()->isSized())
+            BaseAlign = TD->getABITypeAlignment(AI->getAllocatedType());
+        } else if (GlobalValue *GV = dyn_cast<GlobalVariable>(Base)) {
+          BaseAlign = GV->getAlignment();
+          if (BaseAlign == 0 && GV->getType()->getElementType()->isSized())
+            BaseAlign = TD->getABITypeAlignment(GV->getType()->getElementType());
+        }
+        Assert1((!BaseAlign || Align <= MinAlign(BaseAlign, Offset)),
+                "Undefined behavior: Memory reference address is misaligned",
+                &I);
+      }
     }
   }
 }

diff --git a/llvm/test/Other/lint.ll b/llvm/test/Other/lint.ll
index c84f56f8f694dda781c301d60fbfe6e95001b3f9..f6787e973ed761b5f4cd66d849905023491e0aea 100644 (file)
--- a/llvm/test/Other/lint.ll
+++ b/llvm/test/Other/lint.ll
@@ -11,6 +11,8 @@ declare void @one_arg(i32)
 @CG = constant i32 7
 
 define i32 @foo() noreturn {
+  %buf = alloca i8
+  %buf2 = alloca {i8, i8}, align 2
 ; CHECK: Caller and callee calling convention differ
   call void @bar()
 ; CHECK: Null pointer dereference
@@ -26,8 +28,10 @@ define i32 @foo() noreturn {
 ; CHECK: Address one pointer dereference
   store i32 0, i32* inttoptr (i64 1 to i32*)
 ; CHECK: Memory reference address is misaligned
-  %x = inttoptr i32 1 to i32*
-  load i32* %x, align 4
+  store i8 0, i8* %buf, align 2
+; CHECK: Memory reference address is misaligned
+  %gep = getelementptr {i8, i8}* %buf2, i32 0, i32 1
+  store i8 0, i8* %gep, align 2
 ; CHECK: Division by zero
   %sd = sdiv i32 2, 0
 ; CHECK: Division by zero