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Clean up comments for dessa
This commit is contained in:
Gu, Junjie
2023-01-10 20:39:52 +00:00
committed by igcbot
parent ca45856f51
commit 6e359a7e64
1 changed files with 16 additions and 13 deletions
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29
IGC/Compiler/CISACodeGen/DeSSA.cpp
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@ -351,15 +351,14 @@ bool DeSSA::runOnFunction(Function& MF)
// been visited before the aliaser instruction. For example,
// x = bitcast y
// The def of y should be visited before visiting this bitcast inst.
// Let alias(v0, v1) denote that v0 is an alias to v1. DF dominance-tree
// traversal may not handle aliasing in the following order:
// Let alias(v0, v1) denote that v0 is an alias to v1. This visiting order
// under DF dominance-tree traversal will not see aliasing in the following
// order:
// alias(v0, v1)
// alias(v1, v2)
// rather, it must be in the order
// alias(v1, v2)
// alias(v0, v1)
// By doing DF dominance-tree traversal, this kind of aliasing chain will
// be handled directly.
//
// 2. Set up InsEltMap, which coalesces vector values used in InsertElement
// instructions. It is treated as "alias", meaning the root value's
@ -367,13 +366,17 @@ bool DeSSA::runOnFunction(Function& MF)
// AliasMap and InsEltMap is that AliasMap is pure alias in that all
// aliasers have the same values as its aliasee (single-valued, like SSA);
// while InsElt has multiple-valued values. This difference does not matter
// in dessa, but it would matter when handling sub-vector aliasing later.
// in dessa, but it would matter when handling sub-vector aliasing after
// dessa (VariableReuseAnaysis uses experimental sub-vector aliasing under
// the key whose default is off).
//
// We could remove InsEltMap by adding each value into DeSSA node. To do
// so, dessa traversal needs to be modified to have def of those values
// in PhiSrcDefs. This will generally have a larger CC, which means more
// compiling time.
// 3. Make sure DeSSA node only use the node value, that is, given value V,
// We could remove InsEltMap/AliasMap by adding each value into DeSSA node.
// To do so, the dessa algo needs to be improved to isolate them together
// if they need to be isolated. It also may involve several subtle changes
// in implementation. Also, adding all values instead of a single one into
// CC increases the size of CC, which could increase compiling time. With
// this, let us stay with insEltMap (as well as aliasMap).
// 3. Make sure DeSSA node only use the 'node value', that is, given value V,
// its Node value:
// V_aliasee = AliasMap[V] if V is in map, or V otherwise
// node_value = InsEltMap[V_aliasee] if in InsEltMap; or V_aliasee
@ -1210,8 +1213,8 @@ void DeSSA::CoalesceAliasInstForBasicBlock(BasicBlock* Blk)
BBI != BBE; ++BBI) {
Instruction* I = &(*BBI);
// Now, better to think of code as a sequence Codegen Patterns,
// not a sequence of llvm instructions.
// We are after patternmatch, would it make more sense to
// iterate all patterns instead of instructions ?
if (!CG->NeedInstruction(*I)) {
continue;
}
@ -1236,7 +1239,7 @@ void DeSSA::CoalesceAliasInstForBasicBlock(BasicBlock* Blk)
// alias(V1, V0)
// alias(V2, V0)
// ......
// alias(V0, V0) <-- V0 is the root!
// alias(Vn, V0) <-- V0 is the root!
//
// Note that elements could be sparse like
// V0 = InsElt Undef, S1, 1