diff options
author | Sanjay Patel <spatel@rotateright.com> | 2022-01-12 14:58:24 -0500 |
---|---|---|
committer | Sanjay Patel <spatel@rotateright.com> | 2022-01-12 14:59:43 -0500 |
commit | 6bd127b07916015c8d4f603344f06836abba57d8 (patch) | |
tree | 353ff71ccc1774e97a0f582586f5792c0cdd0ac1 | |
parent | 56f62fbf73a2c0844d7f26ae10f2757aac981a2d (diff) |
[InstSimplify] use knownbits to fold more udiv/urem
We could use knownbits on both operands for even more folds (and there are
already tests in place for that), but this is enough to recover the example
from:
https://github.com/llvm/llvm-project/issues/51934
(the tests are derived from the code in that example)
I am assuming no noticeable compile-time impact from this because udiv/urem
are rare opcodes.
Differential Revision: https://reviews.llvm.org/D116616
-rw-r--r-- | llvm/lib/Analysis/InstructionSimplify.cpp | 10 | ||||
-rw-r--r-- | llvm/test/Transforms/InstSimplify/div.ll | 7 | ||||
-rw-r--r-- | llvm/test/Transforms/InstSimplify/rem.ll | 5 |
3 files changed, 16 insertions, 6 deletions
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp index 7dc709e9e932..2986e0fa4ec1 100644 --- a/llvm/lib/Analysis/InstructionSimplify.cpp +++ b/llvm/lib/Analysis/InstructionSimplify.cpp @@ -1079,6 +1079,16 @@ static bool isDivZero(Value *X, Value *Y, const SimplifyQuery &Q, } // IsSigned == false. + + // Is the unsigned dividend known to be less than a constant divisor? + // TODO: Convert this (and above) to range analysis + // ("computeConstantRangeIncludingKnownBits")? + const APInt *C; + if (match(Y, m_APInt(C)) && + computeKnownBits(X, Q.DL, 0, Q.AC, Q.CxtI, Q.DT).getMaxValue().ult(*C)) + return true; + + // Try again for any divisor: // Is the dividend unsigned less than the divisor? return isICmpTrue(ICmpInst::ICMP_ULT, X, Y, Q, MaxRecurse); } diff --git a/llvm/test/Transforms/InstSimplify/div.ll b/llvm/test/Transforms/InstSimplify/div.ll index c4e07d22e4a9..7eed067b284d 100644 --- a/llvm/test/Transforms/InstSimplify/div.ll +++ b/llvm/test/Transforms/InstSimplify/div.ll @@ -155,10 +155,7 @@ define i32 @not_udiv_constant_dividend_known_smaller_than_divisor(i32 %x) { define i8 @udiv_dividend_known_smaller_than_constant_divisor2(i1 %b) { ; CHECK-LABEL: @udiv_dividend_known_smaller_than_constant_divisor2( -; CHECK-NEXT: [[T0:%.*]] = zext i1 [[B:%.*]] to i8 -; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[T0]], 12 -; CHECK-NEXT: [[R:%.*]] = udiv i8 [[XOR]], 14 -; CHECK-NEXT: ret i8 [[R]] +; CHECK-NEXT: ret i8 0 ; %t0 = zext i1 %b to i8 %xor = xor i8 %t0, 12 @@ -166,6 +163,8 @@ define i8 @udiv_dividend_known_smaller_than_constant_divisor2(i1 %b) { ret i8 %r } +; negative test - dividend can equal 13 + define i8 @not_udiv_dividend_known_smaller_than_constant_divisor2(i1 %b) { ; CHECK-LABEL: @not_udiv_dividend_known_smaller_than_constant_divisor2( ; CHECK-NEXT: [[T0:%.*]] = zext i1 [[B:%.*]] to i8 diff --git a/llvm/test/Transforms/InstSimplify/rem.ll b/llvm/test/Transforms/InstSimplify/rem.ll index 9b7852d50cc4..011f991c9e02 100644 --- a/llvm/test/Transforms/InstSimplify/rem.ll +++ b/llvm/test/Transforms/InstSimplify/rem.ll @@ -187,8 +187,7 @@ define i8 @urem_dividend_known_smaller_than_constant_divisor2(i1 %b) { ; CHECK-LABEL: @urem_dividend_known_smaller_than_constant_divisor2( ; CHECK-NEXT: [[T0:%.*]] = zext i1 [[B:%.*]] to i8 ; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[T0]], 12 -; CHECK-NEXT: [[R:%.*]] = urem i8 [[XOR]], 14 -; CHECK-NEXT: ret i8 [[R]] +; CHECK-NEXT: ret i8 [[XOR]] ; %t0 = zext i1 %b to i8 %xor = xor i8 %t0, 12 @@ -196,6 +195,8 @@ define i8 @urem_dividend_known_smaller_than_constant_divisor2(i1 %b) { ret i8 %r } +; negative test - dividend can equal 13 + define i8 @not_urem_dividend_known_smaller_than_constant_divisor2(i1 %b) { ; CHECK-LABEL: @not_urem_dividend_known_smaller_than_constant_divisor2( ; CHECK-NEXT: [[T0:%.*]] = zext i1 [[B:%.*]] to i8 |