If a flag is not used in current BB, we don't need to
set the modFlag bit on that instruction. Thus the register
allocation stage will not allocate a flag register for it.
No performance impact, as the previous implementation will
expire that flag register immediately.
Signed-off-by: Zhigang Gong <zhigang.g...@intel.com>
---
backend/src/backend/gen_insn_selection.cpp | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/backend/src/backend/gen_insn_selection.cpp
b/backend/src/backend/gen_insn_selection.cpp
index 0cb633f..417354f 100644
--- a/backend/src/backend/gen_insn_selection.cpp
+++ b/backend/src/backend/gen_insn_selection.cpp
@@ -228,6 +228,7 @@ namespace gbe
for (uint32_t childID = 0; childID < childNum; ++childID)
this->child[childID] = NULL;
computeBool = false;
+ isUsed = false;
}
/*! Mergeable are non-root instructions with valid sources */
INLINE void setAsMergeable(uint32_t which) { mergeable|=(1<<which); }
@@ -245,6 +246,8 @@ namespace gbe
uint32_t isRoot:1;
/*! A bool register is used as normal computing sources. */
bool computeBool;
+ /*! is used in this block */
+ bool isUsed;
};
/*! A pattern is a tree to match. This is the general interface for them. For
@@ -1453,6 +1456,7 @@ namespace gbe
(insn.getOpcode() == OP_SEL && srcID != 0)))
child->computeBool = true;
}
+ child->isUsed = true;
} else
dag->child[srcID] = NULL;
}
@@ -1747,8 +1751,10 @@ namespace gbe
sel.MOV_DF(dst, src, sel.selReg(r));
} else {
sel.push();
- if (sel.getRegisterFamily(insn.getDst(0)) == ir::FAMILY_BOOL) {
- sel.curr.physicalFlag = 0;
+ auto dag = sel.regDAG[insn.getDst(0)];
+ if (sel.getRegisterFamily(insn.getDst(0)) == ir::FAMILY_BOOL &&
+ dag->isUsed) {
+ sel.curr.physicalFlag = 0;
sel.curr.flagIndex = (uint16_t)(insn.getDst(0));
sel.curr.modFlag = 1;
}
@@ -1976,7 +1982,8 @@ namespace gbe
}
// Output the binary instruction
- if (sel.getRegisterFamily(insn.getDst(0)) == ir::FAMILY_BOOL) {
+ if (sel.getRegisterFamily(insn.getDst(0)) == ir::FAMILY_BOOL &&
+ dag.isUsed) {
GBE_ASSERT(insn.getOpcode() == OP_AND ||
insn.getOpcode() == OP_OR ||
insn.getOpcode() == OP_XOR);
@@ -2513,7 +2520,7 @@ namespace gbe
switch (type) {
case TYPE_BOOL:
- if (!sel.isScalarReg(insn.getDst(0))) {
+ if (!sel.isScalarReg(insn.getDst(0)) &&
sel.regDAG[insn.getDst(0)]->isUsed) {
sel.curr.modFlag = 1;
sel.curr.physicalFlag = 0;
sel.curr.flagIndex = (uint16_t) insn.getDst(0);
--
1.8.3.2
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