InstSimplify: Compute comparison ranges for left shift instructions

'shl nuw CI, x' produces [CI, CI << CLZ(CI)]
'shl nsw CI, x' produces [CI << CLO(CI)-1, CI] if CI is negative
'shl nsw CI, x' produces [CI, CI << CLZ(CI)-1] if CI is non-negative

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216570 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 666e7f2fa96df6667644be7370c0fccc626c018f..118579d5b72ef18f47ef94bf5cee4caa3261717c 100644 (file)
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1993,6 +1993,22 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
         Upper = Upper + 1;
         assert(Upper != Lower && "Upper part of range has wrapped!");
       }
+    } else if (match(LHS, m_NUWShl(m_ConstantInt(CI2), m_Value()))) {
+      // 'shl nuw CI2, x' produces [CI2, CI2 << CLZ(CI2)]
+      Lower = CI2->getValue();
+      Upper = Lower.shl(Lower.countLeadingZeros()) + 1;
+    } else if (match(LHS, m_NSWShl(m_ConstantInt(CI2), m_Value()))) {
+      if (CI2->isNegative()) {
+        // 'shl nsw CI2, x' produces [CI2 << CLO(CI2)-1, CI2]
+        unsigned ShiftAmount = CI2->getValue().countLeadingOnes() - 1;
+        Lower = CI2->getValue().shl(ShiftAmount);
+        Upper = CI2->getValue() + 1;
+      } else {
+        // 'shl nsw CI2, x' produces [CI2, CI2 << CLZ(CI2)-1]
+        unsigned ShiftAmount = CI2->getValue().countLeadingZeros() - 1;
+        Lower = CI2->getValue();
+        Upper = CI2->getValue().shl(ShiftAmount) + 1;
+      }
     } else if (match(LHS, m_LShr(m_Value(), m_ConstantInt(CI2)))) {
       // 'lshr x, CI2' produces [0, UINT_MAX >> CI2].
       APInt NegOne = APInt::getAllOnesValue(Width);

diff --git a/test/Transforms/InstSimplify/compare.ll b/test/Transforms/InstSimplify/compare.ll
index 27fe1bead2324f0718fba6be0b1fa9e405cad7c6..764d76690e671d7562d85d61521251ada8008f12 100644 (file)
--- a/test/Transforms/InstSimplify/compare.ll
+++ b/test/Transforms/InstSimplify/compare.ll
@@ -982,3 +982,30 @@ define i1 @icmp_known_bits(i4 %x, i4 %y) {
 ; CHECK-LABEL: @icmp_known_bits
 ; CHECK-NEXT: ret i1 false
 }
+
+define i1 @icmp_shl_nuw_1(i64 %a) {
+ %shl = shl nuw i64 1, %a
+ %cmp = icmp ne i64 %shl, 0
+ ret i1 %cmp
+
+; CHECK-LABEL: @icmp_shl_nuw_1
+; CHECK-NEXT: ret i1 true
+}
+
+define i1 @icmp_shl_nsw_neg1(i64 %a) {
+ %shl = shl nsw i64 -1, %a
+ %cmp = icmp sge i64 %shl, 3
+ ret i1 %cmp
+
+; CHECK-LABEL: @icmp_shl_nsw_neg1
+; CHECK-NEXT: ret i1 false
+}
+
+define i1 @icmp_shl_nsw_1(i64 %a) {
+ %shl = shl nsw i64 1, %a
+ %cmp = icmp sge i64 %shl, 0
+ ret i1 %cmp
+
+; CHECK-LABEL: @icmp_shl_nsw_1
+; CHECK-NEXT: ret i1 true
+}