[compiler-rt] f5ad9c2 - [builtins] Write __divmoddi4/__divmodsi4 in terms __udivmod instead of __div and multiply.
Craig Topper via llvm-commits
llvm-commits at lists.llvm.org
Thu Sep 10 08:09:58 PDT 2020
Author: Craig Topper
Date: 2020-09-10T08:08:55-07:00
New Revision: f5ad9c2e0ea60dc5426def7a54f04347a33a952e
URL: https://github.com/llvm/llvm-project/commit/f5ad9c2e0ea60dc5426def7a54f04347a33a952e
DIFF: https://github.com/llvm/llvm-project/commit/f5ad9c2e0ea60dc5426def7a54f04347a33a952e.diff
LOG: [builtins] Write __divmoddi4/__divmodsi4 in terms __udivmod instead of __div and multiply.
Previously we calculating the remainder by multiplying the
quotient and divisor and subtracting from the dividend.
__udivmod can calculate the remainder while calculating the
quotient. We just need to correct the sign afterward.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D87433
Added:
Modified:
compiler-rt/lib/builtins/divmoddi4.c
compiler-rt/lib/builtins/divmodsi4.c
Removed:
################################################################################
diff --git a/compiler-rt/lib/builtins/divmoddi4.c b/compiler-rt/lib/builtins/divmoddi4.c
index 7f333510c003..e7cbbb1aaa30 100644
--- a/compiler-rt/lib/builtins/divmoddi4.c
+++ b/compiler-rt/lib/builtins/divmoddi4.c
@@ -15,7 +15,14 @@
// Returns: a / b, *rem = a % b
COMPILER_RT_ABI di_int __divmoddi4(di_int a, di_int b, di_int *rem) {
- di_int d = __divdi3(a, b);
- *rem = a - (d * b);
- return d;
+ const int bits_in_dword_m1 = (int)(sizeof(di_int) * CHAR_BIT) - 1;
+ di_int s_a = a >> bits_in_dword_m1; // s_a = a < 0 ? -1 : 0
+ di_int s_b = b >> bits_in_dword_m1; // s_b = b < 0 ? -1 : 0
+ a = (a ^ s_a) - s_a; // negate if s_a == -1
+ b = (b ^ s_b) - s_b; // negate if s_b == -1
+ s_b ^= s_a; // sign of quotient
+ du_int r;
+ di_int q = (__udivmoddi4(a, b, &r) ^ s_b) - s_b; // negate if s_b == -1
+ *rem = (r ^ s_a) - s_a; // negate if s_a == -1
+ return q;
}
diff --git a/compiler-rt/lib/builtins/divmodsi4.c b/compiler-rt/lib/builtins/divmodsi4.c
index 402eed22fe7a..a85e2993b4e9 100644
--- a/compiler-rt/lib/builtins/divmodsi4.c
+++ b/compiler-rt/lib/builtins/divmodsi4.c
@@ -16,7 +16,14 @@
// Returns: a / b, *rem = a % b
COMPILER_RT_ABI si_int __divmodsi4(si_int a, si_int b, si_int *rem) {
- si_int d = __divsi3(a, b);
- *rem = a - (d * b);
- return d;
+ const int bits_in_word_m1 = (int)(sizeof(si_int) * CHAR_BIT) - 1;
+ si_int s_a = a >> bits_in_word_m1; // s_a = a < 0 ? -1 : 0
+ si_int s_b = b >> bits_in_word_m1; // s_b = b < 0 ? -1 : 0
+ a = (a ^ s_a) - s_a; // negate if s_a == -1
+ b = (b ^ s_b) - s_b; // negate if s_b == -1
+ s_b ^= s_a; // sign of quotient
+ su_int r;
+ si_int q = (__udivmodsi4(a, b, &r) ^ s_b) - s_b; // negate if s_b == -1
+ *rem = (r ^ s_a) - s_a; // negate if s_a == -1
+ return q;
}
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