The alignment of an sret parameter is known: it must be at least the

alignment of the return type.  Teach the optimizers this.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165226 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 33 insertions, 8 deletions

diff --git a/docs/LangRef.html b/docs/LangRef.html
index 89b9227b72..7ee1418f31 100644
--- a/docs/LangRef.html
+++ b/docs/LangRef.html
@@ -1107,9 +1107,9 @@ declare signext i8 @returns_signed_char()
   <dd>This indicates that the pointer parameter specifies the address of a
       structure that is the return value of the function in the source program.
       This pointer must be guaranteed by the caller to be valid: loads and
-      stores to the structure may be assumed by the callee to not to trap.  This
-      may only be applied to the first parameter. This is not a valid attribute
-      for return values. </dd>
+      stores to the structure may be assumed by the callee to not to trap and
+      to be properly aligned.  This may only be applied to the first parameter.
+      This is not a valid attribute for return values. </dd>
 
   <dt><tt><b><a name="noalias">noalias</a></b></tt></dt>
   <dd>This indicates that pointer values
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 491224a4b6..1004ebcac2 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -308,11 +308,20 @@ void llvm::ComputeMaskedBits(Value *V, APInt &KnownZero, APInt &KnownOne,
   }
   
   if (Argument *A = dyn_cast<Argument>(V)) {
-    // Get alignment information off byval arguments if specified in the IR.
-    if (A->hasByValAttr())
-      if (unsigned Align = A->getParamAlignment())
-        KnownZero = APInt::getLowBitsSet(BitWidth,
-                                         CountTrailingZeros_32(Align));
+    unsigned Align = 0;
+
+    if (A->hasByValAttr()) {
+      // Get alignment information off byval arguments if specified in the IR.
+      Align = A->getParamAlignment();
+    } else if (TD && A->hasStructRetAttr()) {
+      // An sret parameter has at least the ABI alignment of the return type.
+      Type *EltTy = cast<PointerType>(A->getType())->getElementType();
+      if (EltTy->isSized())
+        Align = TD->getABITypeAlignment(EltTy);
+    }
+
+    if (Align)
+      KnownZero = APInt::getLowBitsSet(BitWidth, CountTrailingZeros_32(Align));
     return;
   }
 
diff --git a/test/Transforms/InstCombine/align-addr.ll b/test/Transforms/InstCombine/align-addr.ll
index 27916b9860..4ea1bd9beb 100644
--- a/test/Transforms/InstCombine/align-addr.ll
+++ b/test/Transforms/InstCombine/align-addr.ll
@@ -58,3 +58,19 @@ define double @test2(double* %p, double %n) nounwind {
   store double %n, double* %p
   ret double %t
 }
+
+declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind
+
+declare void @use(i8*)
+
+%struct.s = type { i32, i32, i32, i32 }
+
+define void @test3(%struct.s* sret %a4) {
+; Check that the alignment is bumped up the alignment of the sret type.
+; CHECK: @test3
+  %a4.cast = bitcast %struct.s* %a4 to i8*
+  call void @llvm.memset.p0i8.i64(i8* %a4.cast, i8 0, i64 16, i32 1, i1 false)
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %a4.cast, i8 0, i64 16, i32 4, i1 false)
+  call void @use(i8* %a4.cast)
+  ret void
+}