diff options
| -rw-r--r-- | llvm/lib/Transforms/Utils/BypassSlowDivision.cpp | 20 | ||||
| -rw-r--r-- | llvm/test/Transforms/CodeGenPrepare/NVPTX/bypass-slow-div.ll | 77 |
2 files changed, 7 insertions, 90 deletions
diff --git a/llvm/lib/Transforms/Utils/BypassSlowDivision.cpp b/llvm/lib/Transforms/Utils/BypassSlowDivision.cpp index 4aed897d641..d6c31f282e8 100644 --- a/llvm/lib/Transforms/Utils/BypassSlowDivision.cpp +++ b/llvm/lib/Transforms/Utils/BypassSlowDivision.cpp @@ -339,6 +339,11 @@ Optional<QuotRemPair> FastDivInsertionTask::insertFastDivAndRem() { Value *Dividend = SlowDivOrRem->getOperand(0); Value *Divisor = SlowDivOrRem->getOperand(1); + if (isa<ConstantInt>(Divisor)) { + // Keep division by a constant for DAGCombiner. + return None; + } + VisitedSetTy SetL; ValueRange DividendRange = getValueRange(Dividend, SetL); if (DividendRange == VALRNG_LIKELY_LONG) @@ -354,9 +359,7 @@ Optional<QuotRemPair> FastDivInsertionTask::insertFastDivAndRem() { if (DividendShort && DivisorShort) { // If both operands are known to be short then just replace the long - // division with a short one in-place. Since we're not introducing control - // flow in this case, narrowing the division is always a win, even if the - // divisor is a constant (and will later get replaced by a multiplication). + // division with a short one in-place. IRBuilder<> Builder(SlowDivOrRem); Value *TruncDividend = Builder.CreateTrunc(Dividend, BypassType); @@ -366,16 +369,7 @@ Optional<QuotRemPair> FastDivInsertionTask::insertFastDivAndRem() { Value *ExtDiv = Builder.CreateZExt(TruncDiv, getSlowType()); Value *ExtRem = Builder.CreateZExt(TruncRem, getSlowType()); return QuotRemPair(ExtDiv, ExtRem); - } - - if (isa<ConstantInt>(Divisor)) { - // If the divisor is not a constant, DAGCombiner will convert it to a - // multiplication by a magic constant. It isn't clear if it is worth - // introducing control flow to get a narrower multiply. - return None; - } - - if (DividendShort && !isSignedOp()) { + } else if (DividendShort && !isSignedOp()) { // If the division is unsigned and Dividend is known to be short, then // either // 1) Divisor is less or equal to Dividend, and the result can be computed diff --git a/llvm/test/Transforms/CodeGenPrepare/NVPTX/bypass-slow-div.ll b/llvm/test/Transforms/CodeGenPrepare/NVPTX/bypass-slow-div.ll index 4d824e450ff..4846d52f4d2 100644 --- a/llvm/test/Transforms/CodeGenPrepare/NVPTX/bypass-slow-div.ll +++ b/llvm/test/Transforms/CodeGenPrepare/NVPTX/bypass-slow-div.ll @@ -27,80 +27,3 @@ define void @rem_only(i64 %a, i64 %b, i64* %retptr) { store i64 %d, i64* %retptr ret void } - -; CHECK-LABEL: @udiv_by_constant( -define i64 @udiv_by_constant(i32 %a) { -; CHECK-NEXT: [[A_ZEXT:%.*]] = zext i32 [[A:%.*]] to i64 -; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[A_ZEXT]] to i32 -; CHECK-NEXT: [[TMP2:%.*]] = udiv i32 [[TMP1]], 50 -; CHECK-NEXT: [[TMP3:%.*]] = zext i32 [[TMP2]] to i64 -; CHECK-NEXT: ret i64 [[TMP3]] - - %a.zext = zext i32 %a to i64 - %wide.div = udiv i64 %a.zext, 50 - ret i64 %wide.div -} - -; CHECK-LABEL: @urem_by_constant( -define i64 @urem_by_constant(i32 %a) { -; CHECK-NEXT: [[A_ZEXT:%.*]] = zext i32 [[A:%.*]] to i64 -; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[A_ZEXT]] to i32 -; CHECK-NEXT: [[TMP2:%.*]] = urem i32 [[TMP1]], 50 -; CHECK-NEXT: [[TMP3:%.*]] = zext i32 [[TMP2]] to i64 -; CHECK-NEXT: ret i64 [[TMP3]] - - %a.zext = zext i32 %a to i64 - %wide.div = urem i64 %a.zext, 50 - ret i64 %wide.div -} - -; Negative test: instead of emitting a runtime check on %a, we prefer to let the -; DAGCombiner transform this division by constant into a multiplication (with a -; "magic constant"). -; -; CHECK-LABEL: @udiv_by_constant_negative_0( -define i64 @udiv_by_constant_negative_0(i64 %a) { -; CHECK-NEXT: [[WIDE_DIV:%.*]] = udiv i64 [[A:%.*]], 50 -; CHECK-NEXT: ret i64 [[WIDE_DIV]] - - %wide.div = udiv i64 %a, 50 - ret i64 %wide.div -} - -; Negative test: while we know the dividend is short, the divisor isn't. This -; test is here for completeness, but instcombine will optimize this to return 0. -; -; CHECK-LABEL: @udiv_by_constant_negative_1( -define i64 @udiv_by_constant_negative_1(i32 %a) { -; CHECK-NEXT: [[A_ZEXT:%.*]] = zext i32 [[A:%.*]] to i64 -; CHECK-NEXT: [[WIDE_DIV:%.*]] = udiv i64 [[A_ZEXT]], 8589934592 -; CHECK-NEXT: ret i64 [[WIDE_DIV]] - - %a.zext = zext i32 %a to i64 - %wide.div = udiv i64 %a.zext, 8589934592 ;; == 1 << 33 - ret i64 %wide.div -} - -; URem version of udiv_by_constant_negative_0 -; -; CHECK-LABEL: @urem_by_constant_negative_0( -define i64 @urem_by_constant_negative_0(i64 %a) { -; CHECK-NEXT: [[WIDE_DIV:%.*]] = urem i64 [[A:%.*]], 50 -; CHECK-NEXT: ret i64 [[WIDE_DIV]] - - %wide.div = urem i64 %a, 50 - ret i64 %wide.div -} - -; URem version of udiv_by_constant_negative_1 -; -; CHECK-LABEL: @urem_by_constant_negative_1( -define i64 @urem_by_constant_negative_1(i32 %a) { -; CHECK-NEXT: [[A_ZEXT:%.*]] = zext i32 [[A:%.*]] to i64 -; CHECK-NEXT: [[WIDE_DIV:%.*]] = urem i64 [[A_ZEXT]], 8589934592 -; CHECK-NEXT: ret i64 [[WIDE_DIV]] - - %a.zext = zext i32 %a to i64 - %wide.div = urem i64 %a.zext, 8589934592 ;; == 1 << 33 - ret i64 %wide.div -} |
