Subzero: Strength-reduce mul by certain constants. These all appear to some degree in spec2k. This is implemented for i8/i16/i32 types. It is done as part of core lowering, so in theory all optimization levels could benefit, but it is explicitly disabled for Om1/O0 to keep things simple there. While clang appears to strength-reduce udiv/urem by a constant power of 2, for some reason it does not always strength-reduce multiplies (given that they appear in the spec2k bitcode). For multiplies by 3, 5, or 9, we can make use of the lea instruction. We can do combinations of shift and lea to multiply by other constants, e.g. 100=5*5*4. If too many operations would be required, just give up and use the mul instruction. BUG= https://code.google.com/p/nativeclient/issues/detail?id=4095 R=jpp@chromium.org, jvoung@chromium.org Review URL: https://codereview.chromium.org/1146803002
diff --git a/crosstest/test_strengthreduce.cpp b/crosstest/test_strengthreduce.cpp new file mode 100644 index 0000000..b6be659 --- /dev/null +++ b/crosstest/test_strengthreduce.cpp
@@ -0,0 +1,30 @@ +//===- subzero/crosstest/test_strengthreduce.cpp - Strength reduction -----===// +// +// The Subzero Code Generator +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// Implementation for crosstesting strength reduction. +// +//===----------------------------------------------------------------------===// + +#include "test_strengthreduce.h" + +// TODO(stichnot): Extend to i16 and i8 types, and also test the +// commutativity transformations. This may require hand-generating +// .ll files, because of C/C++ integer promotion rules for arithmetic, +// and because clang prefers to do its own commutativity +// transformation. + +#define X(constant, suffix) \ + uint32_t multiplyByConst##suffix(uint32_t Val) { \ + return Val * (uint32_t)constant; \ + } \ + int32_t multiplyByConst##suffix(int32_t Val) { \ + return Val * (int32_t)constant; \ + } +CONST_TABLE +#undef X