[llvm] b58eda3 - [ValueTracking] Fix computeConstantRange to use "may" instead of "always" semantics for llvm.assume

[Nikita Popov via llvm-commits]

Author: Chang-Sun Lin, Jr
Date: 2021-08-02T22:20:17+02:00
New Revision: b58eda39eb1fcb7df942c8569d031a342fa1308d

URL: https://github.com/llvm/llvm-project/commit/b58eda39eb1fcb7df942c8569d031a342fa1308d
DIFF: https://github.com/llvm/llvm-project/commit/b58eda39eb1fcb7df942c8569d031a342fa1308d.diff

LOG: [ValueTracking] Fix computeConstantRange to use "may" instead of "always" semantics for llvm.assume

ValueTracking should allow for value ranges that may satisfy
llvm.assume, instead of restricting the ranges only to values that
will always satisfy the condition.

Differential Revision: https://reviews.llvm.org/D107298

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp
    llvm/unittests/Analysis/ValueTrackingTest.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 522d21812c6a5..b146f07bbaab5 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -7037,7 +7037,7 @@ ConstantRange llvm::computeConstantRange(const Value *V, bool UseInstrInfo,
       ConstantRange RHS = computeConstantRange(Cmp->getOperand(1), UseInstrInfo,
                                                AC, I, Depth + 1);
       CR = CR.intersectWith(
-          ConstantRange::makeSatisfyingICmpRegion(Cmp->getPredicate(), RHS));
+          ConstantRange::makeAllowedICmpRegion(Cmp->getPredicate(), RHS));
     }
   }
 

diff  --git a/llvm/unittests/Analysis/ValueTrackingTest.cpp b/llvm/unittests/Analysis/ValueTrackingTest.cpp
index e8b1a189531f7..c07c76c0b3ced 100644
--- a/llvm/unittests/Analysis/ValueTrackingTest.cpp
+++ b/llvm/unittests/Analysis/ValueTrackingTest.cpp
@@ -2073,7 +2073,7 @@ TEST_F(ValueTrackingTest, ComputeConstantRange) {
     //  * x.1 >= 5
     //  * x.2 < x.1
     //
-    // stride = [0, 5)
+    // stride = [0, -1)
     auto M = parseModule(R"(
   declare void @llvm.assume(i1)
 
@@ -2088,17 +2088,45 @@ TEST_F(ValueTrackingTest, ComputeConstantRange) {
     Function *F = M->getFunction("test");
 
     AssumptionCache AC(*F);
+    Value *X1 = &*(F->arg_begin());
     Value *X2 = &*std::next(F->arg_begin());
 
     Instruction *I = &findInstructionByName(F, "stride.plus.one");
-    ConstantRange CR1 = computeConstantRange(X2, true, &AC, I);
-    EXPECT_EQ(0, CR1.getLower());
-    EXPECT_EQ(5, CR1.getUpper());
+    ConstantRange CR1 = computeConstantRange(X1, true, &AC, I);
+    ConstantRange CR2 = computeConstantRange(X2, true, &AC, I);
+
+    EXPECT_EQ(5, CR1.getLower());
+    EXPECT_EQ(0, CR1.getUpper());
+
+    EXPECT_EQ(0, CR2.getLower());
+    EXPECT_EQ(0xffffffff, CR2.getUpper());
 
     // Check the depth cutoff results in a conservative result (full set) by
     // passing Depth == MaxDepth == 6.
-    ConstantRange CR2 = computeConstantRange(X2, true, &AC, I, 6);
-    EXPECT_TRUE(CR2.isFullSet());
+    ConstantRange CR3 = computeConstantRange(X2, true, &AC, I, 6);
+    EXPECT_TRUE(CR3.isFullSet());
+  }
+  {
+    // Assumptions:
+    //  * x.2 <= x.1
+    auto M = parseModule(R"(
+  declare void @llvm.assume(i1)
+
+  define i32 @test(i32 %x.1, i32 %x.2) {
+    %lt = icmp ule i32 %x.2, %x.1
+    call void @llvm.assume(i1 %lt)
+    %stride.plus.one = add nsw nuw i32 %x.1, 1
+    ret i32 %stride.plus.one
+  })");
+    Function *F = M->getFunction("test");
+
+    AssumptionCache AC(*F);
+    Value *X2 = &*std::next(F->arg_begin());
+
+    Instruction *I = &findInstructionByName(F, "stride.plus.one");
+    ConstantRange CR1 = computeConstantRange(X2, true, &AC, I);
+    // If we don't know the value of x.2, we don't know the value of x.1.
+    EXPECT_TRUE(CR1.isFullSet());
   }
 }