[InstSimplify] add nuw %x, C2 must be at least C2

Use the fact that add nuw always creates a larger bit pattern when
trying to simplify comparisons.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245638 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index ae9d6664fb86f992f46588e276ef738321ea74d2..b6d4c02a9eb1473b378b08eced57c7475d6343e2 100644 (file)
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -2360,6 +2360,9 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     } else if (match(LHS, m_And(m_Value(), m_ConstantInt(CI2)))) {
       // 'and x, CI2' produces [0, CI2].
       Upper = CI2->getValue() + 1;
+    } else if (match(LHS, m_NUWAdd(m_Value(), m_ConstantInt(CI2)))) {
+      // 'add nuw x, CI2' produces [CI2, UINT_MAX].
+      Lower = CI2->getValue();
     }
     if (Lower != Upper) {
       ConstantRange LHS_CR = ConstantRange(Lower, Upper);

diff --git a/test/Transforms/InstSimplify/compare.ll b/test/Transforms/InstSimplify/compare.ll
index 07c90d8f1eb87feafb8e81e59f9760b4ca4c8b51..6e66fbfede9f4e333c7f3d4b207b6097ba34ff6f 100644 (file)
--- a/test/Transforms/InstSimplify/compare.ll
+++ b/test/Transforms/InstSimplify/compare.ll
@@ -1164,3 +1164,11 @@ define i1 @tautological8(i32 %A, i32 %B) {
 ; CHECK-LABEL: @tautological8(
 ; CHECK: ret i1 false
 }
+
+define i1 @tautological9(i32 %x) {
+  %add = add nuw i32 %x, 13
+  %cmp = icmp ne i32 %add, 12
+  ret i1 %cmp
+; CHECK-LABEL: @tautological9(
+; CHECK: ret i1 true
+}