soft-fp64/fadd: Massively split the live range of zFrac0 and zFrac1

The main purpose of this commit is to prepare for "soft-fp64/fadd: Move
common code out of both branches of an if-statement".

Results on the 308 shaders extracted from the fp64 portion of the OpenGL
CTS:

Tiger Lake and Ice Lake had similar results. (Tiger Lake shown)
total instructions in shared programs: 822766 -> 817327 (-0.66%)
instructions in affected programs: 760943 -> 755504 (-0.71%)
helped: 74
HURT: 0
helped stats (abs) min: 8 max: 515 x̄: 73.50 x̃: 51
helped stats (rel) min: 0.58% max: 1.10% x̄: 0.77% x̃: 0.73%
95% mean confidence interval for instructions value: -91.17 -55.83
95% mean confidence interval for instructions %-change: -0.81% -0.74%
Instructions are helped.

total cycles in shared programs: 6816791 -> 6822826 (0.09%)
cycles in affected programs: 6384809 -> 6390844 (0.09%)
helped: 0
HURT: 74
HURT stats (abs)   min: 6 max: 1179 x̄: 81.55 x̃: 50
HURT stats (rel)   min: 0.02% max: 0.17% x̄: 0.09% x̃: 0.09%
95% mean confidence interval for cycles value: 48.99 114.12
95% mean confidence interval for cycles %-change: 0.09% 0.10%
Cycles are HURT.

Reviewed-by: Matt Turner <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4142>

1 files changed, 12 insertions, 3 deletions

diff --git a/src/compiler/glsl/float64.glsl b/src/compiler/glsl/float64.glsl
index 46cae0a4cdb..6208a37757e 100644
--- a/src/compiler/glsl/float64.glsl
+++ b/src/compiler/glsl/float64.glsl
@@ -676,11 +676,11 @@ __fadd64(uint64_t a, uint64_t b)
    uint bFracHi = __extractFloat64FracHi(b);
    int aExp = __extractFloat64Exp(a);
    int bExp = __extractFloat64Exp(b);
-   uint zFrac0 = 0u;
-   uint zFrac1 = 0u;
    int expDiff = aExp - bExp;
    if (aSign == bSign) {
-      uint zFrac2 = 0u;
+      uint zFrac0;
+      uint zFrac1;
+      uint zFrac2;
       int zExp;
       bool orig_exp_diff_is_zero = (expDiff == 0);
 
@@ -736,6 +736,9 @@ __fadd64(uint64_t a, uint64_t b)
       __shortShift64Left(aFracHi, aFracLo, 10, aFracHi, aFracLo);
       __shortShift64Left(bFracHi, bFracLo, 10, bFracHi, bFracLo);
       if (0 < expDiff) {
+         uint zFrac0;
+         uint zFrac1;
+
          if (aExp == 0x7FF) {
             bool propagate = (aFracHi | aFracLo) != 0u;
             return mix(a, __propagateFloat64NaN(a, b), propagate);
@@ -750,6 +753,9 @@ __fadd64(uint64_t a, uint64_t b)
          return __normalizeRoundAndPackFloat64(aSign, zExp - 10, zFrac0, zFrac1);
       }
       if (expDiff < 0) {
+         uint zFrac0;
+         uint zFrac1;
+
          if (bExp == 0x7FF) {
             bool propagate = (bFracHi | bFracLo) != 0u;
             return mix(__packFloat64(aSign ^ 0x80000000u, 0x7ff, 0u, 0u), __propagateFloat64NaN(a, b), propagate);
@@ -770,6 +776,9 @@ __fadd64(uint64_t a, uint64_t b)
       }
       bExp = mix(bExp, 1, aExp == 0);
       aExp = mix(aExp, 1, aExp == 0);
+
+      uint zFrac0 = 0;
+      uint zFrac1 = 0;
       bool zexp_normal = false;
       uint sign_of_difference = 0;
       if (bFracHi < aFracHi) {