[llvm] r275036 - Teach computeKnownBits to look through returned-argument functions

[Hal Finkel via llvm-commits]

Author: hfinkel
Date: Sun Jul 10 21:25:14 2016
New Revision: 275036

URL: http://llvm.org/viewvc/llvm-project?rev=275036&view=rev
Log:
Teach computeKnownBits to look through returned-argument functions

If a function is known to return one of its arguments, we can use that in order
to compute known bits of the return value.

Differential Revision: http://reviews.llvm.org/D9397

Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp
    llvm/trunk/test/Transforms/InstCombine/align-attr.ll

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=275036&r1=275035&r2=275036&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Sun Jul 10 21:25:14 2016
@@ -1279,11 +1279,16 @@ static void computeKnownBitsFromOperator
   }
   case Instruction::Call:
   case Instruction::Invoke:
+    // If range metadata is attached to this call, set known bits from that,
+    // and then intersect with known bits based on other properties of the
+    // function.
     if (MDNode *MD = cast<Instruction>(I)->getMetadata(LLVMContext::MD_range))
       computeKnownBitsFromRangeMetadata(*MD, KnownZero, KnownOne);
-    // If a range metadata is attached to this IntrinsicInst, intersect the
-    // explicit range specified by the metadata and the implicit range of
-    // the intrinsic.
+    if (Value *RV = CallSite(I).getReturnedArgOperand()) {
+      computeKnownBits(RV, KnownZero2, KnownOne2, Depth + 1, Q);
+      KnownZero |= KnownZero2;
+      KnownOne |= KnownOne2;
+    }
     if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
       switch (II->getIntrinsicID()) {
       default: break;

Modified: llvm/trunk/test/Transforms/InstCombine/align-attr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/align-attr.ll?rev=275036&r1=275035&r2=275036&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/align-attr.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/align-attr.ll Sun Jul 10 21:25:14 2016
@@ -13,3 +13,16 @@ entry:
 ; CHECK: ret i32
 }
 
+define i32 @foo2(i32* align 32 %a) #0 {
+entry:
+  %v = call i32* @func1(i32* %a)
+  %0 = load i32, i32* %v, align 4
+  ret i32 %0
+
+; CHECK-LABEL: @foo2
+; CHECK-DAG: load i32, i32* %v, align 32
+; CHECK: ret i32
+}
+
+declare i32* @func1(i32* returned) nounwind
+