This is the last one in a series of patches to support better code generation for bitfield insert.
BitPermutationSelector already support ISD::ZERO_EXTEND but not TRUNCATE.
This patch adds support for ISD:TRUNCATE in BitPermutationSelector.
For example of this test case,
struct s64b {
int a:4;
int b:16;
int c:24;
};
void bitfieldinsert64b(struct s64b *p, unsigned char v) {
p->b = v;
}
the selection DAG loos like:
t14: i32,ch = load<(load 4 from %ir.0)> t0, t2, undef:i64
t18: i32 = and t14, Constant:i32<-1048561>
t4: i64,ch = CopyFromReg t0, Register:i64 %1
t22: i64 = AssertZext t4, ValueType:ch:i8
t23: i32 = truncate t22
t16: i32 = shl nuw nsw t23, Constant:i32<4>
t19: i32 = or t18, t16
t20: ch = store<(store 4 into %ir.0)> t14:1, t19, t2, undef:i64
By handling truncate in the BitPermutationSelector, we can use information from AssertZext when selecting t19 and skip the mask operation corresponding to t18.
So the generated sequences with and without this patch are
without this patch
rlwinm 5, 5, 0, 28, 11 # corresponding to t18
rlwimi 5, 4, 4, 20, 27
with this patch
rlwimi 5, 4, 4, 12, 27
Differential Revision: https://reviews.llvm.org/D49076
llvm-svn: 350118
The current BitPermutationSelector generates a code to build a value by tracking two types of bits: ConstZero and Variable.
ConstZero means a bit we need to mask off and Variable is a bit we copy from an input value.
This patch add third type of bits VariableKnownToBeZero caused by AssertZext node or zero-extending load node.
VariableKnownToBeZero means a bit comes from an input value, but it is known to be already zero. So we do not need to mask them.
VariableKnownToBeZero enhances flexibility to group bits, since we can avoid redundant masking for these bits.
This patch also renames "HasZero" to "NeedMask" since now we may skip masking even when we have zeros (of type VariableKnownToBeZero).
Differential Revision: https://reviews.llvm.org/D48025
llvm-svn: 344347
BitPermutationSelector builds the output value by repeating rotate-and-mask instructions with input registers.
Here, we may avoid one rotate instruction if we start building from an input register that does not require rotation.
For example of the test case bitfieldinsert.ll, it first rotates left r4 by 8 bits and then inserts some bits from r5 without rotation.
This can be executed by one rlwimi instruction, which rotates r4 by 8 bits and inserts its bits into r5.
This patch adds a check for rotation amounts in the comparator used in sorting to process the input without rotation first.
Differential Revision: https://reviews.llvm.org/D47765
llvm-svn: 334011
Hiroshi Inoue