[llvm] b865960 - [ValueTracking] compute knownbits from `(icmp upred X (and/or X, Y))`; NFC

[Noah Goldstein via llvm-commits]

Author: Noah Goldstein
Date: 2024-04-11T12:27:10-05:00
New Revision: b8659600c3af6e5f1a5dd51ac59d6ab2554603d8

URL: https://github.com/llvm/llvm-project/commit/b8659600c3af6e5f1a5dd51ac59d6ab2554603d8
DIFF: https://github.com/llvm/llvm-project/commit/b8659600c3af6e5f1a5dd51ac59d6ab2554603d8.diff

LOG: [ValueTracking] compute knownbits from `(icmp upred X (and/or X, Y))`; NFC

`(icmp uge/ugt (and X, Y), C)` implies both `(icmp uge/ugt X, C)` and
`(icmp uge/ugt Y, C)`. We can use this to deduce leading ones in `X`.

`(icmp ule/ult (or X, Y), C)` implies both `(icmp ule/ult X, C)` and
`(icmp ule/ult Y, C)`. We can use this to deduce leading zeros in `X`.

Closes #86059

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp
    llvm/test/Transforms/InstCombine/known-bits.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 3a10de72a27562..eb8925c5347537 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -701,13 +701,26 @@ static void computeKnownBitsFromCmp(const Value *V, CmpInst::Predicate Pred,
     break;
   }
   default:
-    const APInt *Offset = nullptr;
-    if (match(LHS, m_CombineOr(m_V, m_AddLike(m_V, m_APInt(Offset)))) &&
-        match(RHS, m_APInt(C))) {
-      ConstantRange LHSRange = ConstantRange::makeAllowedICmpRegion(Pred, *C);
-      if (Offset)
-        LHSRange = LHSRange.sub(*Offset);
-      Known = Known.unionWith(LHSRange.toKnownBits());
+    if (match(RHS, m_APInt(C))) {
+      const APInt *Offset = nullptr;
+      if (match(LHS, m_CombineOr(m_V, m_AddLike(m_V, m_APInt(Offset))))) {
+        ConstantRange LHSRange = ConstantRange::makeAllowedICmpRegion(Pred, *C);
+        if (Offset)
+          LHSRange = LHSRange.sub(*Offset);
+        Known = Known.unionWith(LHSRange.toKnownBits());
+      }
+      // X & Y u> C -> X u> C && Y u> C
+      if ((Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE) &&
+          match(LHS, m_c_And(m_V, m_Value()))) {
+        Known.One.setHighBits(
+            (*C + (Pred == ICmpInst::ICMP_UGT)).countLeadingOnes());
+      }
+      // X | Y u< C -> X u< C && Y u< C
+      if ((Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE) &&
+          match(LHS, m_c_Or(m_V, m_Value()))) {
+        Known.Zero.setHighBits(
+            (*C - (Pred == ICmpInst::ICMP_ULT)).countLeadingZeros());
+      }
     }
     break;
   }
@@ -9448,11 +9461,22 @@ void llvm::findValuesAffectedByCondition(
           }
         }
       } else {
-        // Handle (A + C1) u< C2, which is the canonical form of
-        // A > C3 && A < C4.
-        if (match(A, m_AddLike(m_Value(X), m_ConstantInt())) &&
-            match(B, m_ConstantInt()))
-          AddAffected(X);
+        if (match(B, m_ConstantInt())) {
+          // Handle (A + C1) u< C2, which is the canonical form of
+          // A > C3 && A < C4.
+          if (match(A, m_AddLike(m_Value(X), m_ConstantInt())))
+            AddAffected(X);
+
+          Value *Y;
+          // X & Y u> C -> X >u C && Y >u C
+          // X | Y u< C -> X u< C && Y u< C
+          if (ICmpInst::isUnsigned(Pred) &&
+              (match(A, m_And(m_Value(X), m_Value(Y))) ||
+               match(A, m_Or(m_Value(X), m_Value(Y))))) {
+            AddAffected(X);
+            AddAffected(Y);
+          }
+        }
 
         // Handle icmp slt/sgt (bitcast X to int), 0/-1, which is supported
         // by computeKnownFPClass().

diff  --git a/llvm/test/Transforms/InstCombine/known-bits.ll b/llvm/test/Transforms/InstCombine/known-bits.ll
index 30c18cebb2a3ba..fea2f647ee2a81 100644
--- a/llvm/test/Transforms/InstCombine/known-bits.ll
+++ b/llvm/test/Transforms/InstCombine/known-bits.ll
@@ -550,8 +550,7 @@ define i8 @test_icmp_or(i8 %n, i8 %n2, i8 %other) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i8 [[N_OR]], 32
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 0
 ; CHECK:       if.else:
 ; CHECK-NEXT:    ret i8 [[OTHER:%.*]]
 ;
@@ -577,8 +576,7 @@ define i8 @test_icmp_or2(i8 %n, i8 %n2, i8 %other) {
 ; CHECK:       if.then:
 ; CHECK-NEXT:    ret i8 [[OTHER:%.*]]
 ; CHECK:       if.else:
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 0
 ;
 entry:
   %n_or = or i8 %n, %n2
@@ -650,8 +648,7 @@ define i8 @test_icmp_and(i8 %n, i8 %n2, i8 %other) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i8 [[N_AND]], -33
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 32
 ; CHECK:       if.else:
 ; CHECK-NEXT:    ret i8 [[OTHER:%.*]]
 ;
@@ -677,8 +674,7 @@ define i8 @test_icmp_and2(i8 %n, i8 %n2, i8 %other) {
 ; CHECK:       if.then:
 ; CHECK-NEXT:    ret i8 [[OTHER:%.*]]
 ; CHECK:       if.else:
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 32
 ;
 entry:
   %n_and = and i8 %n, %n2