[llvm] r292239 - [ValueTracking] recognize a 'not' of an assumed condition as false

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Tue Jan 17 12:15:49 2017
New Revision: 292239

URL: http://llvm.org/viewvc/llvm-project?rev=292239&view=rev
Log:
[ValueTracking] recognize a 'not' of an assumed condition as false

Also, add the corresponding match to the AssumptionCache's 'Affected Values' list.

Differential Revision: https://reviews.llvm.org/D28485


Modified:
    llvm/trunk/lib/Analysis/AssumptionCache.cpp
    llvm/trunk/lib/Analysis/ValueTracking.cpp
    llvm/trunk/test/Transforms/InstCombine/assume.ll
    llvm/trunk/test/Transforms/InstCombine/select.ll

Modified: llvm/trunk/lib/Analysis/AssumptionCache.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/AssumptionCache.cpp?rev=292239&r1=292238&r2=292239&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/AssumptionCache.cpp (original)
+++ llvm/trunk/lib/Analysis/AssumptionCache.cpp Tue Jan 17 12:15:49 2017
@@ -47,9 +47,11 @@ void AssumptionCache::updateAffectedValu
     } else if (auto *I = dyn_cast<Instruction>(V)) {
       Affected.push_back(I);
 
-      if (I->getOpcode() == Instruction::BitCast ||
-          I->getOpcode() == Instruction::PtrToInt) {
-        auto *Op = I->getOperand(0);
+      // Peek through unary operators to find the source of the condition.
+      Value *Op;
+      if (match(I, m_BitCast(m_Value(Op))) ||
+          match(I, m_PtrToInt(m_Value(Op))) ||
+          match(I, m_Not(m_Value(Op)))) {
         if (isa<Instruction>(Op) || isa<Argument>(Op))
           Affected.push_back(Op);
       }

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=292239&r1=292238&r2=292239&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Tue Jan 17 12:15:49 2017
@@ -553,6 +553,13 @@ static void computeKnownBitsFromAssume(c
       KnownOne.setAllBits();
       return;
     }
+    if (match(Arg, m_Not(m_Specific(V))) &&
+        isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+      assert(BitWidth == 1 && "assume operand is not i1?");
+      KnownZero.setAllBits();
+      KnownOne.clearAllBits();
+      return;
+    }
 
     // The remaining tests are all recursive, so bail out if we hit the limit.
     if (Depth == MaxDepth)

Modified: llvm/trunk/test/Transforms/InstCombine/assume.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/assume.ll?rev=292239&r1=292238&r2=292239&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/assume.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/assume.ll Tue Jan 17 12:15:49 2017
@@ -176,13 +176,13 @@ define i32 @icmp2(i32 %a) #0 {
   ret i32 %lnot.ext
 }
 
-; FIXME: If the 'not' of a condition is known true, then the condition must be false. 
+; If the 'not' of a condition is known true, then the condition must be false.
 
 define i1 @assume_not(i1 %cond) {
 ; CHECK-LABEL: @assume_not(
 ; CHECK-NEXT:    [[NOTCOND:%.*]] = xor i1 [[COND:%.*]], true
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[NOTCOND]])
-; CHECK-NEXT:    ret i1 [[COND]]
+; CHECK-NEXT:    ret i1 false
 ;
   %notcond = xor i1 %cond, true
   call void @llvm.assume(i1 %notcond)

Modified: llvm/trunk/test/Transforms/InstCombine/select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/select.ll?rev=292239&r1=292238&r2=292239&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/select.ll Tue Jan 17 12:15:49 2017
@@ -1344,14 +1344,13 @@ define i8 @assume_cond_true(i1 %cond, i8
   ret i8 %sel
 }
 
-; FIXME: computeKnownBitsFromAssume() should understand the 'not' of an assumed condition.
+; computeKnownBitsFromAssume() understands the 'not' of an assumed condition.
 
 define i8 @assume_cond_false(i1 %cond, i8 %x, i8 %y) {
 ; CHECK-LABEL: @assume_cond_false(
 ; CHECK-NEXT:    [[NOTCOND:%.*]] = xor i1 %cond, true
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[NOTCOND]])
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 %cond, i8 %x, i8 %y
-; CHECK-NEXT:    ret i8 [[SEL]]
+; CHECK-NEXT:    ret i8 %y
 ;
   %notcond = xor i1 %cond, true
   call void @llvm.assume(i1 %notcond)