forked from OSchip/llvm-project
2 Commits
| Author | SHA1 | Message | Date |
|---|---|---|---|
Bill Schmidt
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34af5e1c76 |
[PowerPC] Add an MI SSA peephole pass.
This patch adds a pass for doing PowerPC peephole optimizations at the MI level while the code is still in SSA form. This allows for easy modifications to the instructions while depending on a subsequent pass of DCE. Both passes are very fast due to the characteristics of SSA. At this time, the only peepholes added are for cleaning up various redundancies involving the XXPERMDI instruction. However, I would expect this will be a useful place to add more peepholes for inefficiencies generated during instruction selection. The pass is placed after VSX swap optimization, as it is best to let that pass remove unnecessary swaps before performing any remaining clean-ups. The utility of these clean-ups are demonstrated by changes to four existing test cases, all of which now have tighter expected code generation. I've also added Eric Schweiz's bugpoint-reduced test from PR25157, for which we now generate tight code. One other test started failing for me, and I've fixed it (test/Transforms/PlaceSafepoints/finite-loops.ll) as well; this is not related to my changes, and I'm not sure why it works before and not after. The problem is that the CHECK-NOT: of "statepoint" from test1 fails because of the "statepoint" in test2, and so forth. Adding a CHECK-LABEL in between keeps the different occurrences of that string properly scoped. llvm-svn: 252651 |
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Bill Schmidt
|
15deb803b4 |
[PPC64LE] More improvements to VSX swap optimization
This patch allows VSX swap optimization to succeed more frequently. Specifically, it is concerned with common code sequences that occur when copying a scalar floating-point value to a vector register. This patch currently handles cases where the floating-point value is already in a register, but does not yet handle loads (such as via an LXSDX scalar floating-point VSX load). That will be dealt with later. A typical case is when a scalar value comes in as a floating-point parameter. The value is copied into a virtual VSFRC register, and then a sequence of SUBREG_TO_REG and/or COPY operations will convert it to a full vector register of the class required by the context. If this vector register is then used as part of a lane-permuted computation, the original scalar value will be in the wrong lane. We can fix this by adding a swap operation following any widening SUBREG_TO_REG operation. Additional COPY operations may be needed around the swap operation in order to keep register assignment happy, but these are pro forma operations that will be removed by coalescing. If a scalar value is otherwise directly referenced in a computation (such as by one of the many XS* vector-scalar operations), we currently disable swap optimization. These operations are lane-sensitive by definition. A MentionsPartialVR flag is added for use in each swap table entry that mentions a scalar floating-point register without having special handling defined. A common idiom for PPC64LE is to convert a double-precision scalar to a vector by performing a splat operation. This ensures that the value can be referenced as V[0], as it would be for big endian, whereas just converting the scalar to a vector with a SUBREG_TO_REG operation leaves this value only in V[1]. A doubleword splat operation is one form of an XXPERMDI instruction, which takes one doubleword from a first operand and another doubleword from a second operand, with a two-bit selector operand indicating which doublewords are chosen. In the general case, an XXPERMDI can be permitted in a lane-swapped region provided that it is properly transformed to select the corresponding swapped values. This transformation is to reverse the order of the two input operands, and to reverse and complement the bits of the selector operand (derivation left as an exercise to the reader ;). A new test case that exercises the scalar-to-vector and generalized XXPERMDI transformations is added as CodeGen/PowerPC/swaps-le-5.ll. The patch also requires a change to CodeGen/PowerPC/swaps-le-3.ll to use CHECK-DAG instead of CHECK for two independent instructions that now appear in reverse order. There are two small unrelated changes that are added with this patch. First, the XXSLDWI instruction was incorrectly omitted from the list of lane-sensitive instructions; this is now fixed. Second, I observed that the same webs were being rejected over and over again for different reasons. Since it's sufficient to reject a web only once, I added a check for this to speed up the compilation time slightly. llvm-svn: 242081 |