[InstCombine] conditional sign-extend of high-bit-extract: 'or' pattern.

In this pattern, all the "magic" bits that we'd `add` are all
high sign bits, and in the value we'd be adding to they are all unset,
not unexpectedly, so we can have an `or` there:
https://rise4fun.com/Alive/ups

It is possible that `haveNoCommonBitsSet()` should be taught about this
pattern so that we never have an `add` variant, but the reasoning would
need to be recursive (because of that `select`), so i'm not really sure
that would be worth it just yet.

llvm-svn: 375378

lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -1097,10 +1097,11 @@ static Instruction *foldToUnsignedSaturatedAdd(BinaryOperator &I) {
   return nullptr;
 }
 
-static Instruction *
-canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(
-    BinaryOperator &I, InstCombiner::BuilderTy &Builder) {
+Instruction *
+InstCombiner::canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(
+    BinaryOperator &I) {
   assert((I.getOpcode() == Instruction::Add ||
+          I.getOpcode() == Instruction::Or ||
           I.getOpcode() == Instruction::Sub) &&
          "Expecting add/sub instruction");
 
@@ -1114,7 +1115,7 @@ canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(
                            m_Value(Select))))
     return nullptr;
 
-  // `add` is commutative; but for `sub`, "select" *must* be on RHS.
+  // `add`/`or` is commutative; but for `sub`, "select" *must* be on RHS.
   if (I.getOpcode() == Instruction::Sub && I.getOperand(1) != Select)
     return nullptr;
 
@@ -1140,13 +1141,13 @@ canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(
                                          X->getType()->getScalarSizeInBits()))))
     return nullptr;
 
-  // Sign-extending value can be sign-extended itself if we `add` it,
-  // or zero-extended if we `sub`tract it.
+  // Sign-extending value can be zero-extended if we `sub`tract it,
+  // or sign-extended otherwise.
   auto SkipExtInMagic = [&I](Value *&V) {
-    if (I.getOpcode() == Instruction::Add)
-      match(V, m_SExtOrSelf(m_Value(V)));
-    else
+    if (I.getOpcode() == Instruction::Sub)
       match(V, m_ZExtOrSelf(m_Value(V)));
+    else
+      match(V, m_SExtOrSelf(m_Value(V)));
   };
 
   // Now, finally validate the sign-extending magic.
@@ -1169,7 +1170,7 @@ canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(
   if (!ShouldSignext)
     std::swap(SignExtendingValue, Zero);
 
-  // If we should not perform sign-extension then we must add/subtract zero.
+  // If we should not perform sign-extension then we must add/or/subtract zero.
   if (!match(Zero, m_Zero()))
     return nullptr;
   // Otherwise, it should be some constant, left-shifted by the same NBits we
@@ -1181,10 +1182,10 @@ canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(
              m_Shl(m_Constant(SignExtendingValueBaseConstant),
                    m_ZExtOrSelf(m_Specific(NBits)))))
     return nullptr;
-  // If we `add`, then the constant should be all-ones, else it should be one.
-  if (I.getOpcode() == Instruction::Add
-          ? !match(SignExtendingValueBaseConstant, m_AllOnes())
-          : !match(SignExtendingValueBaseConstant, m_One()))
+  // If we `sub`, then the constant should be one, else it should be all-ones.
+  if (I.getOpcode() == Instruction::Sub
+          ? !match(SignExtendingValueBaseConstant, m_One())
+          : !match(SignExtendingValueBaseConstant, m_AllOnes()))
     return nullptr;
 
   auto *NewAShr = BinaryOperator::CreateAShr(X, LowBitsToSkip,
@@ -1403,8 +1404,7 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
     return V;
 
   if (Instruction *V =
-          canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(
-              I, Builder))
+          canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(I))
     return V;
 
   if (Instruction *SatAdd = foldToUnsignedSaturatedAdd(I))
@@ -2006,8 +2006,7 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
   }
 
   if (Instruction *V =
-          canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(
-              I, Builder))
+          canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(I))
     return V;
 
   if (Instruction *Ext = narrowMathIfNoOverflow(I))

lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -2725,6 +2725,10 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
     }
   }
 
+  if (Instruction *V =
+          canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(I))
+    return V;
+
   return nullptr;
 }
 

lib/Transforms/InstCombine/InstCombineInternal.h

@@ -393,6 +393,8 @@ public:
   Value *reassociateShiftAmtsOfTwoSameDirectionShifts(
       BinaryOperator *Sh0, const SimplifyQuery &SQ,
       bool AnalyzeForSignBitExtraction = false);
+  Instruction *canonicalizeCondSignextOfHighBitExtractToSignextHighBitExtract(
+      BinaryOperator &I);
   Instruction *foldVariableSignZeroExtensionOfVariableHighBitExtract(
       BinaryOperator &OldAShr);
   Instruction *visitAShr(BinaryOperator &I);

test/Transforms/InstCombine/conditional-variable-length-signext-after-high-bit-extract.ll

@@ -57,7 +57,7 @@ define i32 @t0_notrunc_or(i32 %data, i32 %nbits) {
 ; CHECK-NEXT:    call void @use1(i1 [[SHOULD_SIGNEXT]])
 ; CHECK-NEXT:    call void @use32(i32 [[ALL_BITS_EXCEPT_LOW_NBITS]])
 ; CHECK-NEXT:    call void @use32(i32 [[MAGIC]])
-; CHECK-NEXT:    [[SIGNEXTENDED:%.*]] = or i32 [[HIGH_BITS_EXTRACTED]], [[MAGIC]]
+; CHECK-NEXT:    [[SIGNEXTENDED:%.*]] = ashr i32 [[DATA]], [[LOW_BITS_TO_SKIP]]
 ; CHECK-NEXT:    ret i32 [[SIGNEXTENDED]]
 ;
   %low_bits_to_skip = sub i32 32, %nbits
@@ -152,14 +152,14 @@ define i32 @t2_trunc_or(i64 %data, i32 %nbits) {
 ; CHECK-NEXT:    [[HIGH_BITS_EXTRACTED:%.*]] = trunc i64 [[HIGH_BITS_EXTRACTED_WIDE]] to i32
 ; CHECK-NEXT:    [[SHOULD_SIGNEXT:%.*]] = icmp slt i64 [[DATA]], 0
 ; CHECK-NEXT:    [[ALL_BITS_EXCEPT_LOW_NBITS:%.*]] = shl i32 -1, [[NBITS]]
-; CHECK-NEXT:    [[MAGIC:%.*]] = select i1 [[SHOULD_SIGNEXT]], i32 [[ALL_BITS_EXCEPT_LOW_NBITS]], i32 0
 ; CHECK-NEXT:    call void @use32(i32 [[LOW_BITS_TO_SKIP]])
 ; CHECK-NEXT:    call void @use64(i64 [[LOW_BITS_TO_SKIP_WIDE]])
 ; CHECK-NEXT:    call void @use64(i64 [[HIGH_BITS_EXTRACTED_WIDE]])
 ; CHECK-NEXT:    call void @use32(i32 [[HIGH_BITS_EXTRACTED]])
 ; CHECK-NEXT:    call void @use1(i1 [[SHOULD_SIGNEXT]])
 ; CHECK-NEXT:    call void @use32(i32 [[ALL_BITS_EXCEPT_LOW_NBITS]])
-; CHECK-NEXT:    [[SIGNEXTENDED:%.*]] = or i32 [[MAGIC]], [[HIGH_BITS_EXTRACTED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = ashr i64 [[DATA]], [[LOW_BITS_TO_SKIP_WIDE]]
+; CHECK-NEXT:    [[SIGNEXTENDED:%.*]] = trunc i64 [[TMP1]] to i32
 ; CHECK-NEXT:    ret i32 [[SIGNEXTENDED]]
 ;
   %low_bits_to_skip = sub i32 64, %nbits