Factor out alignof expression folding into a separate function and

generalize it to handle more cases.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95045 91177308-0d34-0410-b5e6-96231b3b80d8

lib/VMCore/ConstantFold.cpp

@@ -345,18 +345,19 @@ static Constant *getFoldedSizeOf(const Type *Ty, const Type *DestTy,
       // An empty struct has size zero.
       if (NumElems == 0)
         return ConstantExpr::getNullValue(DestTy);
-      // Check for a struct with all members having the same type.
+      // Check for a struct with all members having the same size.
-      const Type *MemberTy = STy->getElementType(0);
+      Constant *MemberSize =
+        getFoldedSizeOf(STy->getElementType(0), DestTy, true);
       bool AllSame = true;
       for (unsigned i = 1; i != NumElems; ++i)
-        if (MemberTy != STy->getElementType(i)) {
+        if (MemberSize !=
+            getFoldedSizeOf(STy->getElementType(i), DestTy, true)) {
           AllSame = false;
           break;
         }
       if (AllSame) {
         Constant *N = ConstantInt::get(DestTy, NumElems);
-        Constant *E = getFoldedSizeOf(MemberTy, DestTy, true);
+        return ConstantExpr::getNUWMul(MemberSize, N);
-        return ConstantExpr::getNUWMul(E, N);
       }
     }
 
@@ -373,6 +374,62 @@ static Constant *getFoldedSizeOf(const Type *Ty, const Type *DestTy,
   return C;
 }
 
+/// getFoldedAlignOf - Return a ConstantExpr with type DestTy for alignof
+/// on Ty, with any known factors factored out. If Folded is false,
+/// return null if no factoring was possible, to avoid endlessly
+/// bouncing an unfoldable expression back into the top-level folder.
+///
+static Constant *getFoldedAlignOf(const Type *Ty, const Type *DestTy,
+                                  bool Folded) {
+  // The alignment of an array is equal to the alignment of the
+  // array element. Note that this is not always true for vectors.
+  if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
+    Constant *C = ConstantExpr::getAlignOf(ATy->getElementType());
+    C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
+                                                      DestTy,
+                                                      false),
+                              C, DestTy);
+    return C;
+  }
+
+  if (const StructType *STy = dyn_cast<StructType>(Ty)) {
+    // Packed structs always have an alignment of 1.
+    if (STy->isPacked())
+      return ConstantInt::get(DestTy, 1);
+
+    // Otherwise, struct alignment is the maximum alignment of any member.
+    // Without target data, we can't compare much, but we can check to see
+    // if all the members have the same alignment.
+    unsigned NumElems = STy->getNumElements();
+    // An empty struct has minimal alignment.
+    if (NumElems == 0)
+      return ConstantInt::get(DestTy, 1);
+    // Check for a struct with all members having the same alignment.
+    Constant *MemberAlign =
+      getFoldedAlignOf(STy->getElementType(0), DestTy, true);
+    bool AllSame = true;
+    for (unsigned i = 1; i != NumElems; ++i)
+      if (MemberAlign != getFoldedAlignOf(STy->getElementType(i), DestTy, true)) {
+        AllSame = false;
+        break;
+      }
+    if (AllSame)
+      return MemberAlign;
+  }
+
+  // If there's no interesting folding happening, bail so that we don't create
+  // a constant that looks like it needs folding but really doesn't.
+  if (!Folded)
+    return 0;
+
+  // Base case: Get a regular alignof expression.
+  Constant *C = ConstantExpr::getAlignOf(Ty);
+  C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
+                                                    DestTy, false),
+                            C, DestTy);
+  return C;
+}
+
 /// getFoldedOffsetOf - Return a ConstantExpr with type DestTy for offsetof
 /// on Ty and FieldNo, with any known factors factored out. If Folded is false,
 /// return null if no factoring was possible, to avoid endlessly
@@ -401,11 +458,13 @@ static Constant *getFoldedOffsetOf(const Type *Ty, Constant *FieldNo,
       // An empty struct has no members.
       if (NumElems == 0)
         return 0;
-      // Check for a struct with all members having the same type.
+      // Check for a struct with all members having the same size.
-      const Type *MemberTy = STy->getElementType(0);
+      Constant *MemberSize =
+        getFoldedSizeOf(STy->getElementType(0), DestTy, true);
       bool AllSame = true;
       for (unsigned i = 1; i != NumElems; ++i)
-        if (MemberTy != STy->getElementType(i)) {
+        if (MemberSize !=
+            getFoldedSizeOf(STy->getElementType(i), DestTy, true)) {
           AllSame = false;
           break;
         }
@@ -415,8 +474,7 @@ static Constant *getFoldedOffsetOf(const Type *Ty, Constant *FieldNo,
                                                                     DestTy,
                                                                     false),
                                             FieldNo, DestTy);
-        Constant *E = getFoldedSizeOf(MemberTy, DestTy, true);
+        return ConstantExpr::getNUWMul(MemberSize, N);
-        return ConstantExpr::getNUWMul(E, N);
       }
     }
 
@@ -553,22 +611,7 @@ Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,
               if (CI->isOne() &&
                   STy->getNumElements() == 2 &&
                   STy->getElementType(0)->isInteger(1)) {
-                // The alignment of an array is equal to the alignment of the
+                return getFoldedAlignOf(STy->getElementType(1), DestTy, false);
-                // array element. Note that this is not always true for vectors.
-                if (const ArrayType *ATy =
-                    dyn_cast<ArrayType>(STy->getElementType(1))) {
-                  Constant *C = ConstantExpr::getAlignOf(ATy->getElementType());
-                  C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
-                                                                    DestTy,
-                                                                    false),
-                                            C, DestTy);
-                  return C;
-                }
-                // Packed structs always have an alignment of 1.
-                if (const StructType *InnerSTy =
-                      dyn_cast<StructType>(STy->getElementType(1)))
-                  if (InnerSTy->isPacked())
-                    return ConstantInt::get(DestTy, 1);
               }
             }
           // Handle an offsetof-like expression.

test/Other/constant-fold-gep.ll

@@ -64,18 +64,21 @@
 ; PLAIN: @d = constant i64 mul nuw (i64 ptrtoint (double* getelementptr (double* null, i32 1) to i64), i64 11)
 ; PLAIN: @e = constant i64 ptrtoint (double* getelementptr (%1* null, i64 0, i32 2) to i64)
 ; PLAIN: @f = constant i64 1
+; PLAIN: @g = constant i64 ptrtoint (double* getelementptr (%0* null, i64 0, i32 1) to i64)
 ; OPT: @a = constant i64 mul (i64 ptrtoint (double* getelementptr (double* null, i32 1) to i64), i64 2310)
 ; OPT: @b = constant i64 ptrtoint (double* getelementptr (%0* null, i64 0, i32 1) to i64)
 ; OPT: @c = constant i64 mul (i64 ptrtoint (double* getelementptr (double* null, i32 1) to i64), i64 2)
 ; OPT: @d = constant i64 mul (i64 ptrtoint (double* getelementptr (double* null, i32 1) to i64), i64 11)
 ; OPT: @e = constant i64 ptrtoint (double* getelementptr (%1* null, i64 0, i32 2) to i64)
 ; OPT: @f = constant i64 1
+; OPT: @g = constant i64 ptrtoint (double* getelementptr (%0* null, i64 0, i32 1) to i64)
 ; TO: @a = constant i64 18480
 ; TO: @b = constant i64 8
 ; TO: @c = constant i64 16
 ; TO: @d = constant i64 88
 ; TO: @e = constant i64 16
 ; TO: @f = constant i64 1
+; TO: @g = constant i64 8
 
 @a = constant i64 mul (i64 3, i64 mul (i64 ptrtoint ({[7 x double], [7 x double]}* getelementptr ({[7 x double], [7 x double]}* null, i64 11) to i64), i64 5))
 @b = constant i64 ptrtoint ([13 x double]* getelementptr ({i1, [13 x double]}* null, i64 0, i32 1) to i64)
@@ -83,6 +86,7 @@
 @d = constant i64 ptrtoint (double* getelementptr ([13 x double]* null, i64 0, i32 11) to i64)
 @e = constant i64 ptrtoint (double* getelementptr ({double, float, double, double}* null, i64 0, i32 2) to i64)
 @f = constant i64 ptrtoint (<{ i16, i128 }>* getelementptr ({i1, <{ i16, i128 }>}* null, i64 0, i32 1) to i64)
+@g = constant i64 ptrtoint ({double, double}* getelementptr ({i1, {double, double}}* null, i64 0, i32 1) to i64)
 
 ; The target-dependent folder should cast GEP indices to integer-sized pointers.
 
@@ -229,6 +233,10 @@ define i1* @hoo1() nounwind {
 ; PLAIN:   %t = bitcast i64 1 to i64
 ; PLAIN:   ret i64 %t
 ; PLAIN: }
+; PLAIN: define i64 @fg() nounwind {
+; PLAIN:   %t = bitcast i64 ptrtoint (double* getelementptr (%0* null, i64 0, i32 1) to i64)
+; PLAIN:   ret i64 %t
+; PLAIN: }
 ; OPT: define i64 @fa() nounwind {
 ; OPT:   ret i64 mul (i64 ptrtoint (double* getelementptr (double* null, i32 1) to i64), i64 2310)
 ; OPT: }
@@ -247,6 +255,9 @@ define i1* @hoo1() nounwind {
 ; OPT: define i64 @ff() nounwind {
 ; OPT:   ret i64 1
 ; OPT: }
+; OPT: define i64 @fg() nounwind {
+; OPT:   ret i64 ptrtoint (double* getelementptr (%0* null, i64 0, i32 1) to i64)
+; OPT: }
 ; TO: define i64 @fa() nounwind {
 ; TO:   ret i64 18480
 ; TO: }
@@ -265,6 +276,9 @@ define i1* @hoo1() nounwind {
 ; TO: define i64 @ff() nounwind {
 ; TO:   ret i64 1
 ; TO: }
+; TO: define i64 @fg() nounwind {
+; TO:   ret i64 8
+; TO: }
 ; SCEV: Classifying expressions for: @fa
 ; SCEV:   %t = bitcast i64 mul (i64 ptrtoint (double* getelementptr (double* null, i32 1) to i64), i64 2310) to i64 
 ; SCEV:   -->  (2310 * sizeof(double))
@@ -283,6 +297,9 @@ define i1* @hoo1() nounwind {
 ; SCEV: Classifying expressions for: @ff
 ; SCEV:   %t = bitcast i64 1 to i64 
 ; SCEV:   -->  1
+; SCEV: Classifying expressions for: @fg
+; SCEV:   %t = bitcast i64 ptrtoint (double* getelementptr (%0* null, i64 0, i32 1) to i64)
+; SCEV:   -->  alignof(double)
 
 define i64 @fa() nounwind {
   %t = bitcast i64 mul (i64 3, i64 mul (i64 ptrtoint ({[7 x double], [7 x double]}* getelementptr ({[7 x double], [7 x double]}* null, i64 11) to i64), i64 5)) to i64
@@ -308,6 +325,10 @@ define i64 @ff() nounwind {
   %t = bitcast i64 ptrtoint (<{ i16, i128 }>* getelementptr ({i1, <{ i16, i128 }>}* null, i64 0, i32 1) to i64) to i64
   ret i64 %t
 }
+define i64 @fg() nounwind {
+  %t = bitcast i64 ptrtoint ({double, double}* getelementptr ({i1, {double, double}}* null, i64 0, i32 1) to i64) to i64
+  ret i64 %t
+}
 
 ; PLAIN: define i64* @fM() nounwind {
 ; PLAIN:   %t = bitcast i64* getelementptr (i64* null, i32 1) to i64*